Thanks for that guys, all very helpful.
Cylinder head shop looks like the real deal but maybe my sporran is too deep or my arms are too short to be able to take much advantage of their expertise!.
Never thought about a dremel but after offering up an A10 copper gasket, you're right,it doesn't look too difficult to blend in the diameter of the combustion chamber.
The ports are 26mm and they look like they have plenty of scope to blend out to 30mm but maybe 28mm would be more sensible.
I also got an unusual front wheel, I'll get a photo up later on as I have a query about that too.
There is a story to all this. The Dommie was the very first bike I had on the road, in 1961, then sold it and had the usual succession of 60s big bikes. I got the 1958 Road rocket in 1968 and wrote it off fairly spectacularily in early 1970, all cycle parts badly bent but the engine/ gearbox virtually undamaged. Regular road riding came to a halt then and the BSA engine/box went under the bench. Years of trials riding followed, then in 1978, driving up the A9, I saw a guy pushing a british bike and recognised the number as my old Dommie, now a Triton with a very blown motor.
I bought it on the spot and loaded it on the trailer I was towing, and the cycle parts joined the BSA bits under the bench.
Fast forward to 2007, recuperating from heart surgery, and this cafe racer project was born. I had it running last summer, it's in bits again for some tarting up. My intention is to develop it as a conversation piece cafe racer as much as anything, including (don't laugh) a pair of Wal Phillips injectors which are also "under the bench". And yes, I know they can be dodgy, I once saw an Ariel with one on go up in flames after petrol pee'd everywhere.
