You may or may not have a hot cam in that motor...
When I did the V8 swap in my 81 K5, it ran like a pig at first, rough idle, low on power, drank gas, then I followed my friends advice (old school mechanic that forgot more than I'll ever know about cars) in that he told me to advance the timing until it sputtered, then back it off 2-3 degrees, and that made a huge difference! It was originally at 11 degrees and I actually ended up at about 24 before it would quit pinging under load. I had run it out to 32 but it would ping under throttle, but ran amazing just cruising, and 24 was where it would run without pinging at full throttle.
Fully stock other than 10:1 68 Comaro Z/28 heads and a Rochester Q-jet.