Your car looks cool! I like it.
Couple of things to add:
I'd highly recommend either a custom loom as suggested above or a complete loom from a late Volvo 240, when I converted mine I spent a long and frustrating time messing about with the wiring creating a loom from the engine bay section of a late 240 loom and the ecu plug from a 940... not recommended. Unless you really like wiring, take one of the two options above. Chasing electrical faults is frustrating and time consuming.
Your car is early enough that i think the bonnet slam panel will unbolt, remove this before removing the engine it makes things a lot easier. If the slam panel is spotwelded in place, drill those spotwelds out and replace them with bolts to make the slam panel removable.
My 2.5inch downpipe is in place with the steering column in it's normal orientation and the oil to water exchanger from the 940 in place - there isn't loads of space, but it's doable.
Have the cylinderhead skimmed whilst you have the head off the turbo engine to replace the head gasket. Cheap and easy to do when it's in pieces already.
I drove my car with the T cam for a while, then swapped to an A cam - it's a noticeable difference but it isn't night and day. If you're short of time - remember you'll have to reshim the new cam - then leave that for now.
Swapping the aux cam into the engine isn't hard, this youtube video is a bit faffy but covers it. Look at about 18mins for the gear for the oil pump being removed from the second engine, they missed that bit with the first engine.
https://www.youtube.com/watch?v=D738ZeOBIcI
Replace the oil separator as part of the engine refresh.
Note - your local volvo dealer can get all the seals, gaskets, parts you need. I'm on first name terms with the guy at the parts counter at mine
remember the reg number for the 940 to make ordering turbo engine parts easier.
I'll probably think of something else soon enough... good luck!
Cheers