Intake manifold won't seal - How do I check it ?

inertia said

I've run across a few intakes that were bent when they were sucked down over the locator pins, when there was no reciprocal holes in the manifold, front and back..

They sucked oil as you described,, from the bottom of the gskts... also had pin impressions in the manifold..

Click to expand...

Ha, I did that once, cracked a 273 4bbl intake mounting it on a pinned 318. Dough! :-(
Modeling clay works too

You said the intake ports were smaller than the gaskets, like they were overhanging the bottom of the port? You sure you got 360 heads? Sounds like teen heads with 360 gaskets. That won't seal. Just put a bead if modeling clay around the ports and drop the intake on it and snug the bolts. Remove intake and measure how thick the clay us top and bottom, t should be equal ten buy a slightly thicker gasket.