Can I take the big factory AC box out from under the dash without effecting the heater/defroster?
It's a factory AC car, but when it's finished I'm putting all modern stuff it, like Vintage Air.
Thanks

No. The whole housing that contains the heater core and ac evaporator.

Don't the vintage air kits include heater core for defroster. So just run two ducts up to the window defroster vents.

I would keep it. have it rebuilt by classic auto air, and just have the under hood parts replaced by vintage or classic.
The original blower motor and evaporator are better than the new stuff they fit under your dash.

BUT if you are going after the cleaner electronics or no vacuum lines to mess with, then yeah sure pull it and swap in the underdash from one of them.

It is the whole thing as well, in a smaller package.
It has both heat and a/c.
I ran my new lines where the old stuff was.
But if the blower pokes out of the firewall you will have a big hole that needs to be plugged. I know for the ebodies they used to have a plate that let you run your lines there instead.

also not sure how the perfect fit systems are, but I made a mount plate(feets welded) to mount my underdash part to that matched up with the original holes from the old underdash part so I didn't have to cut or drill new holes.
I goofed and never fixed it, because I mounted too high and cannot get the hoses that run for defrost up to the holes in the blower.

I just pulled the unit out of my 68 Valiant do to a leaky heater core. I had to remove the lower dash bolt to get enough room to pry it out, that bad boy is not going back in I going after market now

Not real hard to get in in or out if you use the FSM procedure rather than a wrecking bar and a sawzall.

Thanks guys. I'll leave it in for now. It has a "far from stock" engine in it now, so I'm not sure if I will have enough vacuum for everything to work properly.
I'm just another one of those guys who wants a drag racy type car, with street car comforts like AC.
I do like the sounds of updating from the firewall forward and having the part inside rebuilt.