Changing a TB42 efi and putting a Tb42 Carby in

[the evil twin]

Gday Everyone

We noticed that the raditor was using a fair bit of water very quickly so i assume that the head gasket is gone with this motor.

I was lucky enough to find another engine with the ecu still attached for $300, i will be replacing this engine with that one in the next coming months. Thank you for all your help.

Definitely the best option IMHO and with all the symptoms you now mention I would say 99% sure that all your issues are engine related

Do yourself a favour and, unless you know it is OK for sure, do a compression check on the $300 engine.
If that is OK I would only change the engine at first.
I would also suggest pulling the injectors and getting them serviced.

Those first generation ECU's were very reliable, I wouldn't change one unless I was sure it was knackered.