Do you have a gasket kit for the motor? If it is a 289/302 gasket kit, see whether the intake manifold cork end gaskets fit the contour of the block. If they are too short then you have a 351. If the cork ends fit into the notches of the intake gaskets then somebody has modified your intake.
Reading your first post, you mentioned placing the intake on the motor, did you use gaskets at this point? Without gaskets the intake will not fit correctly, the gaskets are probably 1/8" thick each.
here is a pic of the intake on the motor without gaskets. i dont think the gaskets will fill this gap. Will they? Plus what about the ridge at the top sides of the heads, they dont suppose to meet with the intake Let me know what yall think.
1968 Coupe, Grab-a-trak front and rear suspension, 302 HO, c4, 8 inch rear, 2005 split 5 star rims, making a modded california special.
Don't knock the cork end gaskets, they work if installed correctly. I used the stick on cork end gaskets with a very light skim coat of black RTV on the top where the intake rests and where the cork meets the intake gaskets. 5 years - 5K miles, I had no leaking issues before taking off the intake.