On the 3.2L, I have SSi's and backdated the heat as well as simplified it to simply Defrost. I used Thom Fitzpatrick's FG parts as well as some tin work. (see picture) Came out very clean. I believe you'd be plenty warm in California or Florida at least with a similar system. To remove the air box upfront, you'd need to build a block off plate for the cowl inlet, which I'm going to do soon (so rain doesn't collect in the trunk).
I deleted my controls from the dash and the fan box, footwell mixing boxes, etc. This is a VERY clean solution. I just roll the windows down for vent fresh air and pull the heat levers which control the flapper for defrost / heat. With my SSi's, the defrost is obvious at idle. I think it would work fine in the worst San Diego Winter ;-) At speed it blazes from the defrost ports.
This setup should be easy to test for you and is easy to re-install the stock stuff later.
As far as actually doing the back date in the engine compartment...... When I back-dated the engine tins, I actually reused the Carrera ones on the side, but cut of about 3" to fit those pieces which allow the heater ducts to pass through (measure to be exact, but it is really straightforward - especially if the motor is out. Once I cut them, I had to drill holes to allow the add-on pass through tins to bolt together with my "new" backdated (chopped) Carrera tins. You really only need those pass through pieces + the FG ducting on the fan to back date. I fabricated a plate to cover the hole left by the AC compressor bracket and to cover the hole left by the old blower motor duct. The original pieces had nuts welded on the back side. I just just M6 with nyloc nuts on the back side. Welding the nuts on the backside seemed overkill and would melt the nylon anyways.
Just track down a Left and Right pass through ducting and you are golden. Hope that helps!!
Here are some photos which shed a bit of light.
