Well , today I asked the man himself, David Staton, if it was possible to retrofit his 5:1 output shaft onto one of his older model gearbox...
He said YES!!
As suspected, ya just have to drill thru the left-side cover and swap in his 16-tooth gearbox cog with extended shaft. No other parts needed except his $26.95 output shaft, and using the existing bearing.
I'm so happy.