On the early Scout, the motor pod is roughly 4" x 5" x 2.5" exterior, and is extremely sturdy (steel?) with 1/2" tall cylindrical rubber feet on the bottom. The top plate has a circular mounting for the motor, which appears to be centered in both length and width dimensions. If you can buy one I'm sure you'll have better results than building one. There are other motors, such as the Teres motor which have been used to good effect on the Scout, so it might be worth checking their user forum for tips.
You can and SHOULD buy a Rega template which will show you exactly where you need to mount the tonearm relative to the center spindle. If you get this wrong, the turntable will never play right, it's one of the most critical dimensions. I'd second the recommendation for the Pete Riggle VTA adapter, which will require a larger hole, I think maybe 25mm, but I don't remember for sure. See http://www.vtaf.com/3ptmount.html for more info.
Good luck with the project. The Scout is a nice basis for learning what works, and can be built up to a very high standard.
You can and SHOULD buy a Rega template which will show you exactly where you need to mount the tonearm relative to the center spindle. If you get this wrong, the turntable will never play right, it's one of the most critical dimensions. I'd second the recommendation for the Pete Riggle VTA adapter, which will require a larger hole, I think maybe 25mm, but I don't remember for sure. See http://www.vtaf.com/3ptmount.html for more info.
Good luck with the project. The Scout is a nice basis for learning what works, and can be built up to a very high standard.