I have a set of 500cc blind barrels and pistons from my long stroke 1930 TT Rep. Both are +70thou but worn.
The barrels are otherwise in very good nick and can be re-bored and new 600cc pistons turned down to fit or re-sleeved (the great Eddie Shermer can do this for you if necessary).
The pistons can be turned down to suit barrels that are less than +70thou.
Postage for the barrels will be expensive, as they are very heavy.
In the unlikely event that someone in the club wants them, please make me an offer (tel 01737 554799) ; if not, they will go on Ebay.
When I checked the sizes the pistons/barrels are actually 40thou oversize, not 70thou (a bit of brain fade there).
The barrels have ferrules fitted (existing) and I have new ferrule nuts for them.
About to go on Ebay.