I had the head off my '90 turbo wagon last summer-@ 166K miles, I had a blown, or weak head gasket bettween #3 & #4 , and it eroded the aluminum head, also had minor warpage. The car had been overheated in the past. The turbo was smoking badly at idle occasionally, so i had it gone thru , of course it was 'gutted'.Here's a list, tho not a complete one. The cam belt was just changed, so I left it alone.You should change yours, if you don't know it's history.

cap,rotor, wires, plugs,$94.16
turbo repair,$544.83
injector cleaning,$125.25 ( I think I got hosed on this one)
head repair, weld up eroded area, straighten head, mill, valve job; $459.44
( included gasket set)

I didn't shop around, as I need the car in service, so you could maybe beat these prices. I just asked a mechanic at the Volvo shop who they subbed thier engine work to.So far so good. If I had it to do over, I'd maybe do the rod bearings & rings & maybe replace the oil pump.I'm told you can do these without pulling the engine.