Thanks for the tips guys, I should have at least one of the cork front gaskets lying around and if the intake sits low enough to compress it I'll use that, with RTV of course. If not I'll be extra careful with the RTV bead this time to make sure it covers all the leak points well, build it up in the corners and run it towards the back farther.
@justinp61 I am running PCV but with this heads/block combo I had to make an external rocker oiling setup and I think it's over-oiling the top end and making lots of windage at higher RPM which is splashing on the underside of the intake manifold. The oil flows through custom hollow rocker shaft bolts at the back and I think the hole in them to restrict flow isn't small enough. Next project is to bring some new bolts into work and drill them on our nice lathe with smaller holes.