The aluminium oil tank on my Seeley has a tube welded across the top of it at the back. It has rubber in it, and the front af the tank sits on a rubber pad, on the engine plates. Guys who have not raced much often do not understand the importance of rubber-mounting as much as possible to stop cracking. On a Commando, it is not so bad - the isolastics stop a lot. But I would not use isolastics on a race bike. That connection between your brain,, the handle bars and the rear tyre contact patch is what stops you from crashing. - 'There is a fine line between pleasure and pain' ?
There is a thing which puzzles me about Colin Seeley. For a sidecar guy, he knew a lot about solos. - His frames are magic.
I raced a featherbed Triton for yonks, and I have ridden others as well as a Manx. The Mk3 Seeley is better.
I have not ridden a 1963 Triumph Bonneville, but I can remember them giving the Manxes a run for their money.
The advantage of a Manx is in it's oversteer as you accelerate - it inspires confidence. The Seeley does much more of that.
The problem is, if you ride the Seeley normally, you never suspect what it can really do. With a Manx you find out almost immediately. As soon as you accelerate outb of a corner, you can feel a Manx helping you. With the Seeley, it self-steers a lot in the correct direction,as soon as you gas it when on a lean, often when you have just entered a corner.