Sounds like a good deal for you, I think TLs (in good condition) are worh more.
The hard part is finding the clutch peddle for a 71-73.

 

is there a way to know if what i have in my car now with the 400 is compatible with a 429 including radiator, water pump, fuel pump, wiring harness, etc.?

 

A big block toploader are about 1500 for a busted pos one a c6 maybe 600.The radiator depends which one is in the car right now they could have kept the small block one.The water pump and fuel pump replace them its easier now then later.

 

It looks like i need a torque converter and flywheel for the 71 429 w/c-6 tranny. are they compatible with the 71 400's to where i can use them?