Can I go ahead and install my manifold, turbo, and downpipe and run NA temporarily?
 

nevermind

eh, won't let me delete...alright been thinking about this and I'm just going to wait, pretty sure the NA airbox and crossover piping would be in the way...nevermind...I'll just install my new radiator and intercooler this weekend.

Not really a problem if you keep it out of boost. Trouble is with a GT25 of any size, you're gonna see 2-3psi at heavy throttle above about 4k even with the wastegate arm disconnected.

Go easy on the throttle and make sure you stay out of boost and you'll be fine. It's not recommended however, cause you still need to accelerate fast enough to stay out of trouble... gonna be hard to drive at 50% or less throttle.

if you install the turbo and let it "freewheel" i.e. no load on the compressor side, it will overspeed and die a horrible death.