early model pontiac heads on later block

[crash66030]

I have just built a 400 (1976 block) and I was told that an early set of 389 casting #093 heads would work on the 400 block. It works but the valve train geometry doens't seem to be correct. Has anyone ever done this or known someone who has tried. I need to figure out what to do.

[MrPbody]

The heads will physically fit. The pushrods for the 389 are shorter than the 400. The real question here is: "Why?" What is the purpose? Those 389 heads don't flow near as well, have mount issues (your alternator bracket needs modified to work), have much too small chambers for pump gas, and in general are just the wrong way to go.
Please answer the questions. I'll provide part numbers for the correct pushrods and rocker arms (also different between 400 and 389). I'm just dyin' to know why you would want to do this?
Also, be aware, if your 389 heads are '64 or older, your intake system will also not fit.