both the Mesa and the Marshall are primarily guitar amps, so the OT Fs is designed and chosen with 80Hz low E in mind.
That means bad kind of OT generated distortion with lower frequencies on power output of 10W/40Hz upwards.
The too small OT will act as a natural HPF though, so something good with the bad
They may sound nice, and for some purposes "period correct", but I'd either mod one with a heftier OT, or by reducing the output of the power tubes to half if using for bass instrument.
Choosing an OT with AFe twice the 80Hz one for 40Hz use is a decent rule of thumb, even though it isn't quite that simple.
(AFe being the iron path cross sectional area)