What head gasket for boost? MLS leaking oil

OK on the ARP's. When you say factory torque settings, that is something to pause over..... You don't torque ARP's to the factory torque; you torque them to a significantly higher torque and make sure you use the thread lube every time. Those 2 things together (higher torque AND thread lube) are how the ARP clamping force gets so much higher than standard factory head bolts. The ARP's should have instructions as to the torque to use; and that should be online too.

BTW, do these ARP's have the washer under the nuts too?

I never thought there was a difference between Magnum and LA around the bores; just up around the pushrods. Maybe someone can say better.

Is this a very early Magnum block perchance that still had the oil passages up from the cam bearing #'s 2 & 4? What it perplexing is how the oil in a Magnum could get anywhere around the head gasket except from the lifter valley area, and the drain holes in the heads.

Have you put a pressure gauge on the crankcase and see if you are getting a lot of positive pressure in the crankcase? Intake leaks or ring blowby could be pressurizing the crankcase a bunch.