Mike, I have used all of these manifolds on big block engines....here is my .03 cents (inflation):
most guys back in the day switched out the low-rise for the 163 to gain some extra performance...I think the gains were more noticeable at the track than on the street. I have recently dynoed a 1970 402 witht he flat intake, stock cam, stock car...a little over 430hp...another friend had similar results in the upper 420 range. I'm sure there are another 15-20 ponies in the hi-rise...but, doubt you will feel or see the difference on the street. For a day 2 look the 163 would be my choice over the air gap, since the AG was not available back then....or find one of the older Edelbrock or Weiand units for an aftermarket day 2 style. I have attached a photo of our 70 day 2 with the 163 and the 68 car with airgap and aluminum heads...hope this helps. Let me know if I can help further.
wilma
