These amps aren't that loud compared to modern valve bass heads. Plus, they deliver a clean-ish, but warm sound. IMO, shoving a fuzz through it might give you more of a compressed 'mushy' tone. But I've never tried that approach, so can't confirm.
Also, you're looking at 40-ish year old bits of kit, and reliability is always an issue. And re-valving can be very expensive. Personally, in your band situation, I'd think about a big, modern tranny amp with a valve-driven OD pedal. Maybe give you more headroom to sculpt your sound...
One of the BC experts on massive stacks of valve doom is JoeGarcia - maybe drop him a PM and ask his opinion - I bet he's tried one of these sometime.