You need to buy the proper tools now, Whitworth, you need to buy or download a manual.
Then if you go inside the engine which is easy you need more proper tools.
That engine looks like it hasn't been opened from new, that means it will have a lower chance of some numb nuts having been there (without the proper tools)
It will most likely still have the original bearings, roller drive side, ball on the timing side.
It will also probably have the slotted pistons.
Who knows what be in the sludge trap in the crankshaft.
If you pull the rocker shafts from the head, heat the head, the pins have some interference fit wise, you need a threaded slide hammer for that.
There are other pullers needed if you split the engine cases.
At some point you will find out why it was off the road, not many mint bikes were parked up and left to rot after being picked over.
Maybe it was something minor.
There are simple logics with old Brit bikes, if you go over everything you will be OK, if you get caught up in the bolt shiny $hit to it (paint etc) and don't check the small stuff you will go down the road of many of these old bikes, owner induced problems.
You do not have to replace every part, just make sure it will deliver reliable service, check, check, check and its free for the most part.
The key word is eliminate the bodges if you find them, because a lot of owners were and still are bodger's.
Bodgers are everywhere mind you, here is the camshaft out of my 73 Eldorado. :roll: