acotrel said:
I don't know what barrels fit the 650 Norton bottom end, I don't think any other early Norton had twin carbs ?
The 650cc Norton would accept the parts of any earlier Norton Dominator engine, 750 cylinders/heads will not fit though as to accommodate the larger bore the four rear cylinder studs were moved back and the oil drain-back from the head was relocated, the four main head bolts of the 750 were made smaller in diameter and moved outwards too.
The first regular production Norton twin with twin carburettors would be the Model 99 Nomad Scrambler which was built from 1958-1960, twin carbs were also an option on very late 50s wideline Dominators though.
The 650 Manxman was the first model with the 89mm stroke crank and 1 3/4" crankpins though and the down-draught head. The Atlas and 750/850 Commando were the same as the 650 except for the changes necessary to increase the bore from 68mm to 73/77mm.
The 650 Norton got it's legendary reputation for a few reasons. It was first only available to the USA, which gave it a bit of mystery in it's home market, then when it appeared for sale in the U.K. labeled as the 650ss it tested in magazines at a higher performance all around than the Triumph Bonneville. When the Atlas initially came out in the USA, then in the U.K. a year or so later, it not only had a much lower compression ratio, but was initially supplied with a single carb, so it was not aimed at the performance crowd, plus it's heavier pistons made it shake a bit more too.
Once the Atlas came out in late 62' the 650 was not marketed in the USA too much and sales were very small in comparison. Since the Atlas was not available in the U.K. until 64' the 650ss stayed at the top of the Norton range there and did really well in racing.
Dunstall and others eventually got the bugs out of the 750 and made it fly, but when the Commando came out for 1968 with improvements in it's engine for durability and a lot of marketing hype, the 650ss and 750 featherbed bikes were pushed out of the limelight and faded away.
The motorcycling enthusiasts of the early 60s never heard anything but praise for the 650ss, while the 750 Atlas had a reputation of being slower, vibrating more and having a few bugs like blowing head gaskets and weak cylinders.
So the 650 Norton was a unique package of power and handling just long enough for enthusiasts to notice it's successor's were not so well rounded in comparison. It was the high-point and flag-ship of the original Norton works which was dissolved after 1962.
Presently any 650 Norton is a rare bike. They were made in low numbers to begin with, used hard and blown up then used as raw material for the making of various specials. Any that are left intact are much harder to find top-end parts for than the later 750/850 bikes. Aside from the small bore, most any Commando upgrades/parts will fit giving similar performance and power/reliability.
Some year-by-year 650 Norton facts:
1961 - First official model year. Almost all of 1961 production sent to the USA with the bikes painted almost all blue with red seat covers, small capacity fuel tank, seat moved forwards to suit. Introduced as the "Manxman".
1962 - initial production still sent to USA in the form of all blue/red seat Manxman bikes. 99 of the first 100 650ss bikes were sent to the USA, About half of them looked identical to a Manxman except for having black seats and engines stamped 650ss above the crankcase breather, the other half were still blue but had black frames and seats. Some later 650ss bikes shipped to the usa had the small Manxman tank but the black/silver paint. First year for 650ss and ONLY year it was produced at the original Norton works, a special bike....
About 560 650 Nortons were made before 650ss production kicked in for the 1962 model year, these were the original usa Manxman bikes, by the end of 1962 a bit over 2000 650 Nortons were made at the original Norton works before they were shut down, rare bikes....
1963 - Production small due to parent company AMC abandoning the original Norton works and laying off all workers, moving production to the Matchless works. Specification very similar to 1962 models while AMC used up old Norton stocks of parts. I am not sure at this point if any of the bikes made at the original Norton works late in 1962 were manufactured as 1963 bikes, it may have happened, the Norton records hold the answers.
1964 - 650ss as previous except for many small detail changes to cut production costs. Previous satin-chromed/show chromed hardware largely eliminated for zinc/cad plating. Steering-stop welded on instead of bolt-on. fuel tank filler moved to right side of fuel tank. Smiths Chronometric instruments replaced with magnetic grey-face. Parts detail, material changes from use of new machinery, tooling and jigs too many to list. The later AMC Dominators were not any less functional than before, they were just not to as high a finish and looked a bit more like consumer goods than works of art.
1966 - Continued changes. Upper rear engine plate mounting welded in instead of through-bolted. Oiling system improved with double-speed oil pump gears, larger oilways and pressure-fed rocker arm spindles. Spigot sealing cylinder to head eliminated.
1967- onwards. Amal Concentric carbs phased into production. Head castings same yearly as Atlas and Commando just machined differently for smaller bore etc.. Last hurrah is the single-carb Mercury touring bike sold through 1970, oddly outlasting all other pre-Commando Norton models.
got some new flats at weekend all fitted and looking goood
mechanical wise 
