273 302 318 340 build

Yep, it is an interesting problem with no cheap cure. BTW, let us know when you find a solid cam with less duration than where you are at now. That is going to be a real challenge. Racer Brown ST-2 is the smallest I have run across, with 260 duration that presumably will be down to 255 or less when lashed. With those stock 4 eyebrow pistons, and the 64 cc heads, .028" head gasket, and cam ICL at 106, you are at 8.1/6.95 for SCR/DCR.... you're not there yet IMHO.

Dang, if you would juuust mill those heads .040" to get to 58 cc chambers.... at least your DCR with this ST-2 cam would be at 7.3-7.4.

Looking for other solids.... No, I won't because I suspect I won't find any smaller. I wonder if Racer Brown would do any sort of custom solid for this problem. A lower duration hydraulic would sure make your problem a bit easier to solve. What is the fascination with a solid lifter cam? And of course, a roller would be even better; you can keep the lift and lower the duration. But that is $$$$ too.