I've read through this thread,skimming over the gun parts.I know a guy that still does contracts for the oil industry,standing by people such as 45Brit with a side arm and pump action,while operating in "sensetive" areas.
For me,if I never see another gun or it's efects,it will be too soon.
To the subject in hand.
The Matchless G3 had a Burman CP Type gearbox and clutch,the AMC box was fitted from 1954.
Power output would have been nowhere near 25BHP,a good roadgoing 500 of the time made around 23,a 350 made around 17 BHP.
A ZB350 Goldstar made 25 BHP @ 6000 RPM on an open pipe,a different animal alltogether.
As to the Tug-o-War from a tensioned chain,my money is on the 45.
The OHV requires more revs under drive with the clutch engaged to develope any usable power,it wouldn't make it.
When the flag dropped it would face a test far more severe than starting from any hill in a MCC trial.
Using the "towing with a M20" example (13 BHP) it doesn't hold water.
In the 60's we used to take off on week end trips,it wasn't camping,we took a couple of blankets and slept in bus shelters etc,and eat in cafes.
On returning home one Sunday night,a Norton twin sidecar outfit lunched it's engine,big time.
Also in our party were a couple of 45's.One of the riders called Tiny,he was anything but,tied a rope to his 45 and the outfit carrying Steve and his girlfriend.When he pulled away,it was that easy,Tiny looked round thinking the rope had broke.He towed the outfit the remaining 60 odd miles with no problems.
Thankfully,by the time we reached London,they'd found a compromise on cornering techniques.