A used Centri is going to be easier to install on your car like an old Vortec, etc. If you want a roots style or twin screw, it would be better to swap out your engine with a PI motor instead of doing the full PI swap due to an increase in compression ratio with the PI swap. This is because there were few if any roots blowers and/or twin screw kits out for the 96-98 Mustang and much more out there for the PI cars 99-04.
8 # of boost is decent and I would recommend intercooling so you can get as much power out of it as possible and still have a safe ride in the summer months.
Decide on a horse power goal and which type of blower you want. Then do your research.