[gregneun]

Not sure but I got this:


Motor mount holes

Ok, I didn't say this was easy, but check out the number of drilled motor mount holes on the block. Go ahead get down there and look. Pontiac blocks with only 2 bolts holes per side were cast before 1970. Based on my observations,1964 to 1969 Pontiacs engines were all "2-holers." Blocks cast in 1970 to the last of the run (1978) had 5 holes per side, at least in theory. Some blocks, like my 400 that's in my 79 TA 6.6, is different (below left). It is a 3-holer with two blank pads (no holes). These pads can be drilled and tapped if necessary to accommodate a different engine mount. The other earlier block (to the right) is a "5-holer." These are all drilled and tapped.



from here:
http://www.pontiacstreetperformance..../blockIDa.html