The 1/72 T21 actually has motors in it. The blue label on the can says Hi-Tork 6 Volt, 0.13 Kgcm/Amp, No load speed 5500 rpm, stall current 12A, maximum power 20W at 6.7A and 2700 rpm. Does that ring any bells?? The new Prop Shop props are 52mm 5 bladers on 5mm shafts so I'm wondering how well the 555 motors would cope and how a 555 compares with the units currently installed? I was thinking about using either a 2S or 3S LiPo plus ballast but I guess the original power source was a fairly chunky 6v gel cell?
Opinions much appreciated please!!
I tested & badged those motors about 30 years ago. On the plastic end bells you'll see
low voltage motors ltd You can rely on the motor data.

. Before a switch to electronics I designed 3 phase machines and worked for a couple of major suppliers that got swamped by foreign competition..
You can actually draw a performance graph from these figures I drew up. You can't do anything useful with the performance numbers you quoted from three 555 motors, unless you actually re tested or knew what the actual motors were.
The Hi Tork motors equate to the mfa 540ln or a 540 and 545 geared 2:1.
A 555 manages a bit bigger. 500
size of motor is fine but not a Graupner 500. 540 & 545 would be over propped in direct drive.
So if a tacho says 2750 loaded & 5500 unloaded you are OK but would be better with a 555 or a tiny reduction until the revs are above half the 5500. You are OK on 2s lipo or Li-Ion
I kept a few dozen of the right 555s for my private nest egg but I'm able to replace them now.
PM me if you want 555s matching the RS555-3255 data I posted on Mayhem before.