1957-283 front main seal in neoprean?

[nomad]

Dose any gear head out their know if they are making a neoprene replacement style rear main seal for a 57- 283? The gernal or holder for the seal on a 57 Chev. 283 has the rope shape, and in 1958 the gernal became a" vee" shape with a flat bottom, to except the new and improved neoprene rear main seal. Also is their a benefit to hot tanking the motor prior to a rebuild, compared to cooking it out? Did they make a better breathing ram horn manifold for the corvette283 compared to the 57 passenger car? I have seen vette ones listed at around 2", I believe . do the vette ones have a different angle to the engine pipe? I am soon going to have my 283 motor rebuilt , and I have a set of 1957" power pac 539 heads" I am going to use on my Nomad which was originally a two barrel car.I will have the s/s exhaust inserts installed on the exhaust side, and I am pretty sure that the power pac option use a slightly different cam. Can anyone recommend the best quaility cam, and rebuild parts needed like rings ect?