im taking my 305 heads (lg4)and manifold and putting it on my 87 350 (lo5) i know its already a lower compression motor, im pretty sue i wont have any problems am i right?

 

From feedback I've picked up on this forum as well as some math I've done myself, I can tell you that depending on your pistons you will be running anywhere from 9.5/1 to 12+/1. If your pistons are dished you should be in good shape, otherwise, I'd stay away from the 87 pump.

Also, you will be running out of breath past 4 grand. Most members here will tell you to either get a set of Vortecs or a cheap set of cast performance heads.