Well. Turns out what was fine for mounting a relatively huge 1.8 liter petrol engine doesn't seem to work out too well for mounting a tiny electric motor with gobs and gobs of torque.
After a bit of repair work on the motor mounts and making one of the mounting arms out of 25mm or 1 inch steel tube, the non-hollow type, I proceeded to test the car a little. It all ended quite abruptly with a bang and a gear stick that moves back and forth quite freely, but sideways not at all.
I'm really not converting another car with a transverse engine. Ever.
I didn't have time to look into it. I hope the gear shifter has just dislodged itself from whatever it is supposed to be lodged into. I suppose the worst case scenario is that the transmission is stuck into third gear forever. Not that it's a bad gear to be in. Just that reverse is kind of useful too.
I've come to the conclusion that I need another mount point. Currently the transmission plus motor is mounted to the vehicle at three points. Above the transmission on the driver's side, at the end and quite high above the motor at the other side and at the drive shaft of the right front wheel. This setup seems to leave quite a lot of room for the motor to rock back and forth in the engine bay, which results in all kinds of nasty stuff. The sheer mass of the petrol engine must have kept it at bay originally.
I'm thinking of adding a sort of a torque arm from the motor adapter plate to directly towards either the rear or the front of the car, with a rubber mount at the vehicle side. It's the only way I've come up with so far to stop the damn thing floating about. We'll see what I end up with.
I wonder, which is worse, having a working vehicle which you can't drive on the road, or a vehicle which you could drive on the road, but can't because it's broken?