if theres a leak on the gasket or heads cracked/warped you'd get exhaust gasses forced into the coolant system, hard pipes and pressure in rad, I'd give it a good joinery and blast and see if it settles. did you have the head skimmed? whats the temp gauge do?
Valve stems would give blue smoke on startup, if it's going on it could be head gasket - burning water… Are you losing any? Any smell of fuel in the cooling system? Pressure in there? Could be condensation, as it's getting cold (ambient temp) and it's also been sat have you given it chance to clear out?
Went to look at 2 cars, both claimed to be fine, both had airbag lights up, one had airbag in seat blown and damaged body work bad, pulsating lights, warning lights, bypassed shit haha.
It can be done and there is guides but you won't be able to balance it, and if you know what unbalanced motors do you'll know it can be bad, not to say don't do it, if you want to go for it!