I don't mean to offend, but a stock 305 cam is miniscule and you dramatically lowered the already low compression with the 350 heads. You might be in the low 7's with compression.
You could probably stuff drinking straws in the intake ports and never run out of breath.
The GM intake came installed on millions of ZZ4 crate engines and probably half of those buyers took it off for something else. I bought mine as a new take-off for $40 plus $10 shipping on Ebay.