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A suggestion I’d make is.......

It sounds like the car is running and the OP has driven it around already.

I’d do the basic easy stuff first.
Make sure the timing, jetting, lifter preload is all correct.
Do a compression test on a couple cylinders.

Then before tearing anything apart....... get it on a chassis dyno, or take it to the track for some numbers so you can establish a real “baseline”.

Most chassis dyno shops will have some sort of “no tuning” deal where they’ll strap the car on and make 2-3 pulls for $100.
That’s a good place to start.

I’d suggest a place with a dyno jet, since there are tons of runs to look at from that type of dyno, and they seem to have less variation from dyno jet to dyno jet.