A - it soundz like you want to have a go.
Get an AFR gauge installed and running. Install a dasdaq.

First - swap your 65mm C2 with a Karman 62mm or EC if you want to save $100. You can onsell these later with a new bearing in the pack, there will always be a market.
2nd - get a 178mm and put your 74mm back on.
3rd - keeping your 178 on - put your 65mm back on and gauge your AFR's. =>20psi.
Spend $1000 and install a KC (or trunk ice) and requisite bypass valves around the IC.

4th - if your still moving ahead....try the 178/62 combo with the KC (or ice tank). Also try it with the interior heater on (for add. cooling)...;>)
I dont know if anyone has hit this combo before.
One of the rotors in the SC will be hitting almost 30,000 rpm by that stage - which is way over its OEM spec of 21,644rpm - but just keep that in mind.
You might have to do a few extra hours at work for a new SC some ways down the track - if only to put better bearings in.

b22b