dnb55, I'm running a 91FX on mine but only its inverted, I would almost be willing to bet you would be fine inverted but instead of installing a pitts you instead install a perry pump as I am doing, I have never had a lick of trouble running my 91 upside down with a perry on it. I also don't think you need two gallons through it, one should be just fine on a test stand.

You can grab one of the cheaper brands of fuel for break in as performance would not be an issue.

Also by using the perry pump, it will allow you to place the fuel tank on the CG, again as I have.

As far as mounting the engine inverted I had to drill two small holes on the opposite side of the muffler in the cowl to allow the allen wrench for tightning the muffler screws.

Blackie