[Beaver]

The GT6 had a small 6 cyl pushrod engine and full independent rear suspension. They handled quite well in their day, but the running gear was fragile in my opinion, especially the rear end. You can read that "expensive to fix." And the front end gave waay too much positive camber in corners causing massive understeer (though that can be fixed...) An engine swap would take care of the expense of maintaining a vintage engine/transmission, but a rear axle swap would be a lot of work.
A MG Midget did not have IRS, so the rear axle swap would be easier, IMO. You could put an entire modern drivetrain in one. Might be a good way to go.
Now, the original Mini with a Metro drivetrain... That seems like it might be lots of fun!

But what I know of any of these Austin / British Leyland cars is that they are maintenance-intensive, and something is always coming loose and needing tightened up. For a tinkerer, that is not a big problem though.

As far as the Lucas electrical system, I think someone with some electrical knowledge could build their own full wiring harness and convert much of the electrical system to something much better and more modern. Their electrical systems were very simple by today's standards.

I think it's a great idea by green standards... Reduce, reuse, recycle and restore!

Beaver