I have 1 aircon duct comming out the dash. The others come out through the trans tunnel.
The dryer/blower unit is in the passenger foot well. Passengers legs go under the unit. You can get compact units from Vintage Air.
www.vintageair.com
HPC is a coating yes. HPC seem to be well regarded.
www.hpcoatings.com.au
I have a rear exiting exhaust. I had the whole system done including the mufflers.