Thanx for all the replies and advice.
Intake manifold is Edelbrock Torker (1990 vintage, as was engine build.) I'm liking the idea of a Performer + spread-bore quadrajet of some sort, but will wait till I know all the facts about the engine.
Having done further research I think the engine is probably 396 (4.030" bore x 3.875" stroke) as this seems to be the most usual config at that sort of capacity.
The 1990 vintage Dart II heads appear to have been available in 64cc or 72cc chamber capacity - which is more likely? I'm guessing 64cc.
With 3.875" stroke, 64cc heads and flat top pistons, compression ratio should be around 11.5:1 yes?
I'll check distributor and vacuum advance.
Has thick, good condition spark leads.
I agree that I need to find out for sure what it all is, so I'll get the cam profile, bore, stroke and compression ratio measured when I can get it in the shop (which will be spring when I have my other car back on the road, and hopefully also have a job.)
I quite like the idea of swapping in a used LS engine if I can sell my engine for decent money - I'll keep that idea in mind too.