Help! Swapped 302 heads on my 318.

Ok. Why would they be different? With the springs on? Would the rockers be wrong?
Same springs, rockers and push rods?lt should work fine. Only thing maybe different is the factory valve stem height, taller.
Adjusted properly, it should be fine.
You either have valves hitting pistons or , well for sure have them hanging open because it never pushes air and only sucks