I used the compact vintage air unit and I have the entire unit between the dash and firewall. The only holes in the firewall are for the two heater hoses.
I did not have to move the support brace for the dash.
I also got the built in defroster with the heater and instead of running defrosters, I ran the defroster lines to the footboxes to provide additional heat.
I bought directly from Vintage Air, but you probably could save about $20-$30 if you find a reseller.
[ May 06, 2002, 12:28 PM: Message edited by: kellerscobra ]