@quinnamb3 As Simon says, the Honda ones will be hard to find new now but the 1995-2001 Rover 400/45 should still be available and will be a direct fit. The MGZS ones won't be there though as they never had manual windows, only electric. For converting to electric, yes it can be done. Easiest way would be to find two replacement front door that already have them,as fitting would be a tricky job. I'm doubtful the wiring will be in place though so you would also need the wiring harness from the fusebox to the doors too. Might be worthwhile checking the fuse box to see if it has the fuse slots for the electric windows as not sure if the fuse box will maybe also be different. There might also be relays to add to the fusebox to for the electric windows.Nothing is impossible though!
Really nice MB3 you've got there, looks tidy!