[G6Tanuki]

As an experiment, I wired both transformers in parallel and then loaded them with a bunch of 12V car bulbs [21-Watt brake-light type and 10-watt sidelight type] then left things running for 36 hours.

At the end, both transformers were noticeably warm, but no more so than the mains-transformer of a typical valve radio would get after an afternoon's use [and I suspect modern wire insulation is rather better than the 60-year-old stuff used on something like a Pye P75's transformer].

My 'finger-test' showed no detectable difference in the temperatures of the cores. I'm happy. Yes the issues of peak currents when feeding rectifiers are noted; I will be using a bridge because it uses both halves of the secondary all the time and results in lower peak currents than the old-fasdhioned centre-tapped-secondary-and-two-diodes.