Body Parts Assembly Advice

[magwakeenercew2jh]

the '68 cab and '71 chassis/bed/front clip are all separated. Each in their own "chunk". The motor and trans are out and almost ready to be connected to each other and dropped into the frame.

I moved the cab back about 12" just to have access for the "drop", and while it was there, painted the firewall.

The front "clip" (the sheet metal), including inner fenders and radiator core, grill, hood, etc., are all sitting outside on four sawhorses. The original inners are rusted. Luckily, that's all that's badly rusted on that group of parts.
Today I scored a set of stock inner fenders ($75) and I'm going to paint them the same color as the firewall.

After I gut all the stuff out of the front "clip" (horn, wiring, a/c condenser and lines....the radiator is already out), I'm going to prime and paint the whole compartment the same color as the firewall and inner fenders.

Now the question:

Other than the good advice I got about not tightening up anything yet, what is the best "work flow" of how to take the old inners out and put the new ones in?...

Should I fit them to the front "clip" and lift the whole thing over the motor and on to the radiator core support?

Or should I prime and paint with the old inners in, then take the old ones out and off to the squisher (or someone who might want them) and then put the new ones that are now painted into the front "clip"?

Or should I clean up the new inners, put them on the front "clip, and prime and paint while they are in the "clip"...Then lift the front on as one section?

All of this supposes that I've moved the cab back on to the new mounts and have all that "group" of parts (the cab) in the right place...and not bolted down permanently.

Sorry I don't have the talent or money or energy to try to shave off all the firewall stuff. I DO have a nice new brake booster assembly and a Vintage Air set up coming.
And I'll try to spend some creative time on routing the wiring. But I guess I'll use the holes that GM poked in the wall...I'll look for proper new grommets.

Thanks for any help. I love this stuff.