Yeah, each rotor turn from one plug terminal to another is 30 degrees (360/12=30). And if I remember, that equals 15 degrees of timing? So “hopefully” your plug wires are just one or two off.
If not, then your distributor is several teeth off, and you’ll have to pull it and put it back in. I would get the engine to #1 TDC, and static time it. Been there, done that. A lot of work, but good to get car to square 1.
Or as a hack, you can put your plug wires one off to compensate until you get the right timing.
Sounds like previous owner didn’t get distributor in right. I understand, took me a couple tries. MUCH more difficult than a 4 cylinder engine!
Also, if your engine is truly 30degrees too advanced, I would think the thing would be pinging pretty badly.