That .61 FX will be perfect for it. One warning though, the gap between the firewall and the needle valve is tiny (about 3/4" in fact.) I'd seriously consider getting a fuel dot and fitting an extra fuelling line to the tank, because once that fuel tubing gets coated in engine oil it's going to be a bear to keep taking off/putting on. I plan on removing the tank from mine and outfitting it with a separate fuelling line today.

I purchased my fuel dot from PSP Mfg. They were very quick to ship the order to me, had a great range of milled and annodised Aluminum dots, and the price was right. If you want to take a look, their range of standard sized fuel dots is [link=http://www.pspmfg.com/FuelDotsRegular.html]here.[/link]

Good job on the build so far, by the way! Those wings just fall together, don't they