This is an old, old motor. Even if it has had some freshening, that most probably has not been recent.
Freshening the heads, which is pulling them, having the guides and seats inspected, most likely guide work done, replacement rather than knurling, and new springs and keepers. Hardened seats are required for use of unleaded gas, and it is doubtful that this has had hardened seats installed. This is the perfect time to install a moderate cam, any more on a mild motor is not recommended, but a bit more duration and lift will really wake this motor up. To match the cam, you will need to have the appropriate springs to suit. It won't be a bad azz hot rod, but it will sound and feel like it.
Those factory oval port heads are GREAT heads for a moderate big block, way more desirable than big money heads, as the port size is perfect for maximum port velocity. They will respond incredibly well to a moderate cam. If for some reason someone put the rectangular port heads on it, then you will have an issue as they are way too large for a mild motor, they are too large for a hot motor. I put aftermarket 310CC oval port heads on my 502, healthy cam, 10.2:1 compression and it hit 580hp/578tq on the dyno. I took off factory new rectangular port heads (still have them) as they are too large for any use other than WFO 7,000RPM on the drag strip, that's what they were made for. Verify the heads that are on it before you start in. If the ports are too big, then you lose port velocity, and response suffers. Not only that, but you'll need way more cam to 'crutch' the heads, which leads to other problems. Having the correct port size lets you just cam as you need for performance, and the heads will respond to the cam perfectly, speaking for moderate builds here.
As long as you don't increase the compression, you are fine with unleaded regular, timing set to suit, however.
The motor is out of the car, the perfect time to have it gone over, basic freshening, cleaning and painting, and it will be a sight to behold, as well as a healthy, thumpy cruiser for years to come.
Once it's in, it's a PITA to work on, and you probably won't want to, unless you have issues. Doing it now saves on issues and surprises, and lets you install the motor you really wanted in the first place, with some assurance of no problems. If it's got good compression, you're all set.
Do it right, now, then enjoy it.