Last 420a i built used anaerobic sealant only on the front case, rtv for all corner transitions (vc). Iirc, the oil pan has a silicone anti-crush gasket, and all other gaskets should be steel, paper or graphite-crush style. But it has been a hot minute since then.

Id defer to dsmcrzy, as hes got prolly one of the nicest 420a's ive seen on here, and the fsm holders.

In the end, please dont rtv the hg, or any other intake/front case/oil pans etc.