I don't plan to turbo mine, I'm looking to keep it looking stock so NA it is. I was supposed to get measurements for ARP a few months ago but never had the time so I'm intrigued into the slightly larger ones you found. Oh and the MLS gaskets are perfect, you should shoot me a PM on the cost...
As far as the oil pump, from what I can remember, the spot for the outer ring is larger and deeper then the EA82, and I think the bolt pattern is slightly different. I might be able to get some pictures this weekend of one of my spare engines.
I bought 6 mls gaskets for $120 each from gasketstogo, John can make them from whatever template you want to provide. For future ea82 gaskets, it may be cheaper now.. not sure if he saves the dies/tooling (i would hope he does tho). Give him a call for a quote.
Regarding head studs, there is a 5.5" apr stud that would probably work for both the longs and short, but it only comes in 7/16". I considered trying them, but it might be pushing it for the longs (.25" ball bearing trick to fully seat the stud would work tho). Thought I should mention it if someone wants to do more homework. Getting to 75% torque load 70ft/lbs on the 7/16" is a lot more reasonable, vs 110ft/lbs on 1/2" studs (scares the hell out of me actually).
Re the oil pump. There isn't much meat to go that much deeper into the block, but with some welding it could be done easily. Nncoolg made a post on ausubaru with pictures, it seems doable imho. Hell it might even be possible mill off the pickup/outlet and filter mount.. tap the block and run a bypass filter. But there isn't much room to play with behind the tbelt. Could tap it from inside the pan also and block the front holes. I've been trying not to think about this because I will just want to do a dry sump..
My to do list for the next month or so: (time/money permitting)
build the first longblock
megasquirt v3.0 diy + harness (ahh the fumes)
figure out the fuel system (evo injectors/pump/surge, goodies for e85)
exhaust header (moar fumes)
awic (type 14 + type 118)
I wish I was rich.