Hello
I am installing a new 3800 compressor and AC line into my 88 Fiero. It has an original condenser that doesn't seem to leak. I have installed a new orifice and receiver/dryer.

I have a brand new condenser and also a new evaporator ready to install. Neither of the originals appears to be leaking. Would it make sense to leave them in and save the new parts for the day they start to leak?

Or is it a bad idea to run a new compressor and line with an old condenser & evaporator, in case there are chunks and dirt in there that may contaminate the new compressor? The AC system has been exposed to open air for a while so there is going to be moisture and likely some dirt in there

Moisture in the system is taken care of when vacuuming down the system when closed and unless you are filling it with manually with dirt find it hard to much to get in there when open at the ports. You should flush the old oil out the best you can (if not already converted to R134a) and if you are still worried just add an inline filter available multiple places online.