[Big Will]

Why not mount up the S60 T5 engine into your 98 V70 as suggested? That's a really good motor to use for a project car.

No need to get a T5 ECU. You can either send your 98's ECU to someone to reflash with a tune that suits whatever motor, turbo and injectors you install or they can send you back a modified ECU that you can reflash yourself.

If you do just end up installing the slightly bigger turbo, injectors, and exhaust manifold from the S60 then getting a T5 ECU from a 98 isn't a bad way to make a bit more power. It won't be perfectly matched up to your engine but it'll certainly run well and give you a bit more power. Years ago, I ran a similar setup: 98 V70 AWD (same engine as your GLT) with a 15G turbo, T5 ECU, white injectors (one step up from the stock ones) and a catback exhaust. That setup yielded 218 whp on an AWD Dynojet. I was pleased.