Hi folks
I ordered and received oe replacement manifolds and risers for my 502.
Looks like a straight forward job,
my only question would be whether to install the gaskets dry or with sealant and if so,
what kind?

They can go on dry. I installed mine with a light coating of the Permatex Copper Spray Hi-Temp gasket sealant.

The exhaust gaskets are made to be installed dry, no sealant. If you put selanat on them it will be an ugly mess if you need to replace them. Go dry and draw the bolts up nice and even. Can't remember the torque value but its not huge, the bolts (or studs) are threading into the casting of the block which is much less strong than a nut.