OK, so my first 'modded' Big Muff board is done - I overcooked the gain stages initially by only using a 100Ω resistor between the Emitter and ground of the first 3 tranny stages, then came down gradually to 390Ω, and increased the coupling caps from 100nf to 1µf, but I might try dropping them to 470nf as the bottom end is MAHOOSIVE!!!
Big, fat, dirty muff. What's not to like?