Whats the difference between the 1986 and 1987 manifold base?Do they have different bolt patterns or angels or what?or is there any difference.Thanks

 

The '85 and '86 TPI intake base has the old intake bolt pattern, with holes drilled perpendicular to the intake flange on the head (at a 90° angle), whereas the '87 and later intake base has the center two holes on either side drilled at a 72° angle to allow easier assembly and access, and more room to enlarge the runners.

The intakes can be interchanged with very little modification.