Those are 350 HO heads
They have press in studs that were non adjustable.
If you get a good set of lock nuts that are metal, you could adjust to zero lash and go another quarter turn like you would on every other hydraulic cam.
The stock nuts are made to be torqued down and if you tried to do any sort of adjustment they would back off after a while.
Those heads on a 400 would give you at least 10 to 1 compression which is way to much for today's garbage gas