different hubs, different gear ratios, different axles, different flywheel clutch and pp
Countless other differences, but those are th big ones.
You can bolt an NA tranny to a 3sgte, but the axles will not match up.
The NA tranny is reported to be much weaker than the turbo unit. I will be able to speak to this soon. I have just hitched an NA tranny to a gen3 motor and will be putting them into a mkI. I will be running about 300 rwhp and will gladly report the breakages if and when they occur.