My 2 cents...... The prices to do that engine including installation in a shop is probably within reason. #2 any small block Chevy is the same on outside appearance. So how is a smog tech going to know you have a 305 a 350 or 400 for that matter ? He wont and nobody can possibly know unless they run the casting numbers. I did a similar swap several years ago on a 85 El Camino, replaced a 305 with a ZZ1 350 with a cam up grade. Used all the emission system, Electronic carb & ignition from the 305. Passed Missouri smog with flying colors. Only way anybody could tell it wasn't a 305 was when you hit the gas.