It's the heads that matter, not the block. A Gen 1 SBC block will accept heads from 1955 to the end of the Vortec run in 2002. The heads you have w/the 72 degree center bolt hole angle were used between about 1987 and 1995 except aluminum headed Corvettes.
You can elongate the bolt holes of the intake (some info here
). It's no big deal. But if the intake can be returned for the correct one, that would be the preferred way to go.
Some of these heads were used on TBI equipped truck engines and were called "swirl port"
(or "SP") heads. Casting numbers 14102191 and 14102193 are seen most often. They do not flow well at elevated rpm- like above about 4500 rpm or so on a 350 cid engine. If you have SP heads, consider swapping them out. If you swap them, you might as well bite the bullet and get Vortec heads
if you cannot afford aftermarket heads. The Vortec heads are worth as much as 50 HP more than traditional Gen 1 SBC production heads. They do requi
re a different intake manifold than 1985-back heads, so that's something to consider if you were going to have to buy a new/different intake anyway.