I just--finally--finished a hybrid build. And now I have to sell the car because I'm taking a job overseas. Damn.
Here's what I did:
new water and oil pumps, new tensioner, belt, etc.
Leave the heads alone except for deshrouding and cleaning and checking valves for fit. There is no reason to port and polish because:
Crower springs and retainers
Cosworth cams. The cams are the key. You can port all you want but if you don't have the right cams you are wasting money. The Cosworth cams give my engine all the air it could ever want (unless you are going for stupid horsepower, i.e. more than 600 whp).
Perrin fuel rail
Stock injectors bumped to 810cc by WitchHunter (waaaaay better than PE's)
All major hoses and intake are silicone. Perrin catch can.
Stock intake box with stock Subaru filter (plenty of air. Intake is dismantled to the box, and hole in fender where intake formerly went is closed. All air now comes from the fender. Easy to do, and more effective than anything that gets air from inside the engine compartment. Do not use KN filters. OEM filters are fine unless you are going for more than 500whp).
Aluminum radiator. The stock radiator is not enough.
Blouch TD06-20G turbo. This is more than enough turbo if you are staying under 500whp. Blouch makes a slightly better turbo for another three or four hundred dollars. Call them. They are the best that I've found when it comes to turbos. Also the most cost effective.
I'm using an AVO topmount with AVO bov. Too much gravel and sand on the roads where I live for a front mount. In fact, the car has a spray-on bra for front-end protection. JDM STi hood scoop.
If you stay under 500 whp, the stock ECU is all you need. Dom at getadomtune can give you a good tune over the Net. Best tune is by Dom on Kito's Mustang Dyno at Kito's in Seattle. But anyone with a Mustang Dyno should be able to set you up. If you are on the East Coast, contact Andrewtech for references.
Trans: I put in Albins gears, instead of PPG. Both are comparable, but Albins has a one-piece input shaft instead of two-piece, and is thus a little stronger. If I had to do it again, though, I'd go with PPG because Dan at Andrewtech really knows what he's doing, and because PPG stands behind their product much better.
Clutch is a Clutchmaster's 300 Kevlar. Very smooth. Takes no more effort than OEM clutch.
At the moment mine is tuned to 300 whp/270 wtrq. But this is only because when it was tuned it had stock trans. With no timing to speak of in it, and only 5 pounds of boost (we flashed the ECU as conservatively as possible so we could drive the car over to Seattle to do the tune), first run on the dyno, the engine put out 315whp/over 300 trq. Had to dial it down for fear of shredding the trans on the dyno. Long story short: next tune, I want it at about 400 whp/410wtrq. Remember, this is on a very conservative dyno, perhaps the most conservative in the country. The stock EJ20 heads are good to about 600 whp (with methanol injection).
Option: take out the tumblers. They really are not necessary. I left mine in, but wish I had taken them out.
Hope this helps. Even at 270 wtrq and 300 hp, mine is a monster. Another 100, and it is going to be a handful. At present, with very little timing in it, I'm getting 30 mpg cruising at 70 mph.