...there was no cyl base gasket/ but a residue of liquid gasket goo everywhere.... All rubber orings disintegrated on touch
No cylinder-to-case gasket is utilized. You noted the rubber o-rings, smalls and a large one, that will need to be replaced with fresh.
After thoroughly cleaning the case and cylinder mating surfaces, a tiny dab of sealant may be used on both the case and jug. Note the photo. This little bit is all you need for the engine case. Another little dab'l do you on the jug mating surface. Correctly applied, you should be able to see through the sealant. Keep it evenly coated and thin. If, upon assembly, you can see some squeeze out, you may
have used too much.
Best applied as a film using your finger. Avoid getting the sealer close to the upper studs as there are oil transfers along here going up to the rockers. Choked with sealant, no oil will reach the rockers. That's a bad thing.
Yamabond works well and is available at local Yammerhammer shops. A small tube will last you forever. Lemme see... did I mention applying it thin?