I have tried searching but couldn't find a answer. If I swapped in a series 5 T2 engine would I need the S4 T2 drivetrain or could I just use the S5 drivetrain and use a S4 T2 lsd. Only reason I ask is because I prefer the S4 clutch pack t2 diff over the S5 viscous.

 

You can use your stock N/A Tranny & N/A Differential with a S5 T2 Engine. The only thing you will need to keep/change is your N/A flywheel and bolt it onto the s5 TII Engine.

All TII Drivetrain bolts up to each other no matter what series so you can have a s4TII Tranny bolt up to a s5 TII LSD or vise versa. The only thing you need to worry would be having both N/A and TII drivetrain. If you want to bolt up a N/A Trans to TII Diff you would need a custom driveshaft and vise versa.