Hi Wali, ouch, that must have sounded expensive...
I looked into this a little, a while ago. It was too expensive for me in the way the engineer explained it (and not practical given my riding), but it could be done.
The idea (apparently) is to get flywheels cut from billet and a whole new assembly made up. You can then use your big end of choice.
You can use the Ariel flywheels and have them bored, but they may be your next weak link.
The Jawa big end looks good. Others have used Norton, I think Chris Reynolds uses a Sunbeam assembly in his Hartley VB.
The biggest issue will be finding a rod that is more or less the right length (you could shim the barrel a bit). You can get a Carillo made, but you might have to mortgage your grandmother. http://www.bsagoldstar.co.uk/price_list ... ist_12.pdf
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.