Hi,
I have spent some time with my Flabulanche build and tried different FETs. The build document doesn't mention concrete FET VP values, but as I understood from the ROG article and particularly Jon's posts, the 2N5457s meant to have a VP around 1.5V. I had a bunch of 2N5457 with very low VPs (0.5 V), which made the circuit very gainy.
Also the volume and gain pots are linear ones in the build document. Changing them to audio tapers made my build more useable.
Cheers,
Fuad