AGU/02J into Mk1 ... gearbox options ... 02S?

Hey,
I'm looking for guidance on gearbox and possibly turbo choices for my Mk1 golf (if the longer gearing and turbo should match). The car's in the shop being prepped for paint so I have time to change plans.

I already have a 1999 Mk4 GTI donor car with an 02J gearbox (I think EBD) for which I've bought Epytec engine/gearbox mounts. The immo is defeated.
My calculations suggest the engine will be 3300 rpm for 100 km/hr (based on 170/70R13 circumference), which doesn't sit well for highway. The car had an retro-fitterd 5-speed 020 with low gearing (code 6W, apparently from something called a Rover Maestro), with 100km/hr at 2600rpm. I'd like to get similar gearing if possible.

I've read a lot about 02J diesel gearboxes but Australia didn't get many VW models of the era mentioned by UK and US contributors. My research suggest I should look for codes EBJ, EGR, EUH, DQY and some VR6 variants (VR6 was rare in Aus). Any suggestions what cars these will be found in (I suspect breakers/wreckers won't know if I cite gearbox codes)? Any corrections or alternatives to this list will be much appreciated.

Alternatively, an 02S. More VW types were imported more recently and these include 6-speeds (which I assume are 02S). I understand these are preferred as they have the required lower gearing, particularly for 6th. Is this correct? What cars would likely have the best gearboxes?

But I suspect this just starts the conv.

• I've read that I'll have to swap the cases with the 02J to accommodate the speedo cable … but since it's apart, should I opt for a strengthened LSD and other work?
• I've heard starters and gearbox mounts also differ. Will the 02J-Mk1 Epytec gearbox mounts work after I swap the cases or will that be a difference mount?

Worse comes to worse I can initially use what I've got and change the gearbox later. Should the engine management/turbo change to suit the changed gearing?
The engine has a K03 and was thinking a K03/s hybrid for maybe 250hp. I want it to be an easy everyday driver but also fun. Should I choose the turbo later, after I know the gearing or can (should?) performance be simply changed later via engine management?
Sorry if this is all a bit random but trying to avoid possibly rookie, obvious mistakes