which b20 engines use 6 bolt flywheel& which use 8 bolt?

Change over was very late in '73. Most 'experts' seem to think that all d-jet cars are 6 and k-jet are 8.

is b21 same flywheel as b20?

Yes, indentical until about 83, when the turbos changed the position of the dowels to the mid point between bolts holding the clutch pressure plate on. Then there was a variation using a 1/2 bigger clutch set into the flywheel for later turbos- b23ft and b230ft

.....do b30 engines use same crankshaft for automatic or standard trannie all thru series?

No there are 6 and 8 bolt variations, too. Maybe surprisingly, the flywheel on a b30 is much lighter than a b20. Maybe Volvo thought the crank had enough inertia in itself.... The clutch on a b30 is unique, and bigger diameter than anything that came after including later b230 intercooled turbos

Anyone find mistakes in what I remember...?