Intake Manifold leaks Coolant- Could it be too small??

Looks like an old sanding belt was used. Definitely not production as they were not even machined flat just flat as cast iirc. Your gonna need to get the heads lower (deck the block) or get the intake wider (1/16 spacer or thick *** fiber gaskets or double up on them) and then you'll have to make sure the ports and the bolts line up. Spacers cut from 1/16 (16 gauge) may be easy to make with tin snips and a jig saw. Your kinda screwed on that modded intake. You may want to try 1/16 rolled gasket material and cut your own intakes out of that as they are not that precision or torqued on and use the tall foam China wall gaskets as they are pretty thick uncompressed. Good call on the dowels. Overlooked them once and cracked a 273/4 intake.