Early 273 intake compatibility

#1 The potential issue is the sealing surface not the ports themselves

#2 the OP doesn't tell us what he is installing the manifold on - 273?, 318?, 340/360???

3# it's not just the bolt size, it's the bolt angle!!! Somewhere here I have a thread that measures the angle mismatch and suggests the beveled washer needed to fix it. I'm on the road so can't take time to look myself