After several months of work and pretty big investment in new parts, the Mk10 is back on the road, and I’m posting a few photos and details for those who helped with good advice.
The cooling system is complete with recored modern high efficiency brass radiator along with a custom built aluminum header tank, new hoses and overflow tank. The original steel routing pipe was replaced with copper and formed rubber hoses. The new heater vacuum valve worked until the heater core blew. The box is going to need major rust repair. 
Currently on heater bypass, drivable.
The braking system is overhauled with rebuilt calipers including new pistons all around and new rotors. The obsolete master and booster have been replaced with XJ parts. While I used a series 2 booster in a series 1 can, I recommend sticking with all series 1 parts for any others doing this upgrade, as there was a need for shimming of the mc away from the booster to cure dragging brakes. These are the same brakes as the 420G and I have to say that they are great! I also replaced the missing emergency brake parts and the e-brake is as good as new (fwiw). That’s a salvage reservoir that fits under the bonnet better than the originals, and there are 2lb residual pressure valves in the front and rear lines.
I restored and rebuilt the irs, which was moribund. Shocks were bad and were replaced with adjustable GAZ units. In case anyone else uses these, I have them set on maximum (turn the dial all the way towards the minus sign - go figure) and they see to work very well. Be aware that they come with their own retaining collars and do not use the original shock retaining collets.
A great many other things happened like tuning carburetors, replacing the power steering pump, belts, vacuum and water hoses, correcting electrical faults, driveline bushings, front suspension repair, new suspension boots, speedometer cable, replacement tachometer drive, battery, and a hundred other things. I previously detailed the complete refurbishment of the fuel system including the pumps, senders, and tanks which were in very poor condition.
For now, the transmission is working, not leaking at the moment, but not confidence inspiring. Yet to be done is transmission adjustment, tire replacement, exhaust manifold and gasket refurbishment, completion of paint detailing, front and rear windscreen rubber, door window rubber and electric window repair, air conditioner repair, carpet replacement, and wood refinishing. Should be done by…
Thanks in advance for the advice I know I will need to finish.
has decided bypassing the window cutout switch was a suitable way to deal with it “cutting out”, which is apparently an issue