Follow Up we ended up using FelPro 0.051 head gasket and the NGK '7s

Its absolutely perfect! Thanx to the 12' converter (2000 stall)
which I squeezed into the UltraBell and the beefy handbuild TorqueStrap
it idles relatively smooth. NO issues with detonation, water stays at 160° all day long. It revs up like a 2-Stroke engine. Easily, smooth cruising
but if you push the pedal it revs up and moves like hell. Downshifting into
second gear and you fly! For me its both of two worlds it has the torque to rapdily move the heavy car with the heavy converter and the long 2,76 axle and if you push the pedal it really goes! So far not pushed above 100 Mls as the power lifts the car in second gear. New adjustable shocks needed.

Only downsize...950cfm Carb seems to be to small