Actually I do have something for size comparison:

Thats my hand and I have an average size man hand lol
I'll have to have a look a bit later when I get home on what the actual numbers are on the thing to give an idea of sizing, I'd imagine just one on a 1600 would spool up on idle lol.
When I said about the GTi manifold, I was thinking if you turn it upside down you have the 2 ports pointing upwards, with a little bit of fabrication you could have a little intertube adaptor between the GTi flange and the 2 turbos mounting them close to the head. but higher up than they are normally mounted, then as you suggest you could do anything from there.
Basically I have a mk3 golf 1.8 gas engine, 31mpg is the most I achieved out of it in recent times (I may be driving it too hard) so its a running car that my g/f is getting more experience in with me having not driven for a while so we dont use it all that often, I have a 1.6N/A that I had in my camper, which I upgraded to a TD, I then aquired a TD pump to rebuild for my van (not that there is anything wrong with my TD one thats on there but I wanted to do the mods) and I thought if I do the swaps I will have a 1.6 n/a to rebuild, its got a mk4 golf inlet manifold whack a modded diesel pump on it and then the 2 turbos, then look to install it in the mk3 golf. Need to get a TDi gearbox to raise the gearing too.
That was kinda my plan.
As for the wastegates, I am sure I can unsieze them, but if I cant I could always fit an external wastegate before the turbos.