The usual method is to adapt the drive shaft, not the pinion. We do it in our long bed lathe by machining an adaptor to fit the shaft, which we weld into place.
sorry, that what I was trying to articulate, should I use a drive line to pinion adapter from a solid drive line and machine it to fit and weld it to the tube
This adapter can be used directly to replace coupler or welded onto a tubular or solid driveshaft.
Some people run a shortened solid driveshaft with out center bearing, but I do not have experience with that.
The adapter can be turned to fit inside >120 wall 2" driveshaftn tubing,which is what I did. or use a 34 tube driveshaft
thanks I have another tube shaft it's longer, so i will chop it and have the forty's coupler prof. machined to fit and welded then balanced. is the coupler spring clip needed