Check the block surface for flatness, use a straight edge with a flash light behind it to check if block is flat, minimal light passes under straight edge
I assume the heads have been cleaned and surfaced?
or do the same with heads
If block and heads are flat then nothing is needed except the composite gasket.
The head gaskets metal rings for each cylinder hold back 900+ PSI when a cylinder fires, they are the important part, and RTV or copper spray does nothing for them.
The water jacket holes have 12 - 18 PSI(Rad Cap rating) so not much pressure there
If their are oil passages, not the drains, then they are maybe 40-50psi, which is alot but block or head would need a deformity to leak at those 1 or 2 passages.
So no treatment is needed, IMO
MLS(multi-layered-steel) head gaskets can use a spray on sealer, they are only used with aluminum heads through, they tend to leak when Cold