How much boost you planning on running?
My PTE51 came preassembled and installed with a stock 12 lb. spring when I bought it from Modern Musclecar now perhaps Ramchargers. No clocking no drilling just bolt it on the THDP I bought with it, they also knew how big to make the hole in the exhaust housing another factor to figure in when buying a turbo.
Worth talking to the vendor about all this stuff, me? I just got lucky
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WE4, Daily Driver, PTE51, 43lb. Bosch, THDP race cat., Postons Headers, 21/2"SS Ultraflows and pipes, 16 pos. Maxeffort thumbwheel chip, Bilsteins, Airbags/snubber,snows, 307 adj.reg./ gauges,scamaster and D.S.,BSTC,small stuff too. V4 IS IN!!! Not legal for racing.
GN loaded, mostly stock, car #2. 112K miles. Accufab reg. 160stat.,Scanmaster.