Mk4 GTI donor for Mk1 ... what parts?

Hey all,
I bought a very rough 1999 Mk4 GTI as a donor for my 1976 4-door Mk1. The engine is AGU and the gearbox is 02J.

This sites engine swap guides are a great resource and I can see this is a well trod path. I'm looking for something fun but not necessarily huge power for a car so light, so thinking just engine service and overhaul the turbo to standard (unless I'm told that's silly … I'm a sucker for an upgrade).

I see we lose the power steering pump and the timing belt tensioner swaps out for a manual one (all available in a kit from various web sites) but being in Australia I was hoping to keep the A/C - no point looking cool if you aren't cool.
I was hoping to hide the climatronic evaporator inside/under the dash and replace the factory vent controls with the climatronic head-unit (… looks like single Din). Am I dreaming or risking a nightmare? I'm OK to fettle the underside of the dash, the evaporator and the firewall as long as I can keep the top of the dash looking "genuine"ish. The dash is the original cardboard and vinyl with all the expected sags and splits from the Oz sun and the years - it needs refurbishment so OK to be a little aggressive.

The engine has 200,000Kms (160,000 ish miles?). I'm thinking compression test and if OK just replace timing belt, chain, water pump, seals and gaskets and service turbo while all is accessible. Drop sump and replace oil pump and B/E bearings … maybe valve stem seals while the engine is out. I'll replace seals in the gearbox plus a new clutch. Missed anything?

I read mixed data on the 02J drive flange - I read somewhere the early mk4 GTI has 100mm drive flanges and elsewhere all manuals had 108mm drive flanges. I already have 100mm CV joints, drive shafts, steering knuckles and brakes from a 1985 Mk1 convertible so I need 100mm flanges on the 02J (haven't picked up the donor yet so can't check if 100 or 108).

Also, I can see various sites sell ready-made engine and gearbox mounts to suit this conversion plus swap-out bits to fit the whole enchilada into the Mk1. Unfortunately all in the UK or Europe. Are any the gold standard? Any I should keep away from?

Lastly, what else should I take from the mk4? I speculate the ECU but then I've heard specialist ECUs are better. I've read of rear brake conversions so maybe those? What parts specifically? I'm thinking hydraulic clutch so perhaps need that … good idea?

Mk1 has been in the garage for 10 years. I'll wash and send it to a panel shop for general straightening and fettling. Will post pictures as it progresses.

Cheers,
Tom.