So I have 2 MR2 SW20's ... one N/A, one turbo, about to pull the head off the turbo as I am fairly certain it has corroded and is getting blow by into the water jackets.. I have 2 questions, the engine in the turbo is said to be fully forged, with JE pistons, JE moly rings, Eagle rods with ARP bolts, King race series bearings throughout. Was thinking of spending a few dollars to drop in a steel head gasket instead of a graphite one (worth it or not?), but if so I am also torn between a thickness, I am told that as the engine sits it can run 20lb boost all day.
 
So there is one question... The second is, how much more difficult is it to do a head in the car as opposed to pulling it out?
I have uneven ground to work with so lifting a car is not an easy feat, especially if it only makes the job a little easier.

Sounds like you'll find it difficult either way...
I'll be removing the head off mine soon and at the very least you'll need to remove the manifolds and then deal with the timing belt etc.
 
As for the head gasket, i'd definitely suggest a metal head gasket. If you do though, I'd also suggest some ARP head bolts (I'm assuming you don't already have them). The ARP bolts need re-torquing a second time though, so just bear that in mind (I'm pretty sure it's in the instructions though)

I would be pulling the engine out for that job. It really isn't one you can do in the car. The tension in my SW20 is a bitch to reach and it's extremely difficult to line up everything in the car.

Cylinder headwork is possible in situ - BUT you're going to need to get under the car anyway to access parts of the exhaust/turbo system, so the car is going to have to be raised safely anyway.
 
Give the job some careful thought, and my suggestion would be to move it to somewhere with a concrete floor and room around it.  And if you're going to do that, then you might as well pull the engine and box and make life as easy as possible.  As I've said before that - engine out gives you the chance to do the little jobs that make an MR2 smile . . .

if you are going to run metal head gasket i would also get your head machined at the least i had my block machined as well as a provention of future head gasket issues

Ended up getting a Cometic 1.295mm MLS head gasket, with ARP head studs, it seems that I need to remove the head because the turbo is blowing pressure into the water jackets due to corrosion of the water port, but got a guy says he will weld it up and machine it for $300 AUS which I figure is pretty damn cheap, he also showed me a few other 3SGTE heads he had lying around, with the same damage saying it is fairly common. It still runs fine, just under boost it fills the head with exhaust ... so I have just parked it until I get all the bits n pieces together. Thinking I am going to do it in the car, the timing belt etc wasn't that much of a drama when I did the water pump a little while ago.

almost all 3SGTE engine blocks need to have the top deck macined if you want to sucessfully run a MLS, so good chance engine has to come out.
 
badly corroded heads are not that common with 3S engines. 
 
 

Following on from Terry's comment - a corroded head tends to suggest that the car hasn't enjoyed proper TLC.  Using the CORRECT coolant, and keeping it maintained, is important with any modern engine.  If you're having to do remedial work on the head what condition is the rest of the motor in?
 
" . . . said to be fully forged, with Kryptonite pistons, unobtanium rings, Schaulkelpferd rods with Stuhlgang bolts, . . ."   Are you sure?

Can't be sure until I crack the engine, I can only go by the last mechanics receipts, and well I can't say I put too much faith in that many mechanics... As for the neglect, I have no doubt it has been neglected for a while before I bought the car, plus it was sitting for 3 months, un-started, with plain water instead of coolant, when I found it. But at the price I got it for .... was still worth it.

You'll need the get the deck faced if you don't want combustion gases in your coolant again.  Most MLS headgasket manufacturers recommend 50RA finish, minimum.  I severely doubt the standard finish will suffice.