Seems to me that if you are using a mandrel, you only need to find any bushings that will fit snuggly in whatever the tube is for that pen. Once you have a bushing that fits in the hole, you simply turn the outside diameter using calipers to match the corresponding parts. Turning between cones, is turning between centers. You just mount a 60" center in the drive side and a 60 live center in the tail, instert the tubed blank between the two and spin carefully and lightly because if you tighten the tail too much you will expand the tube causing it to break the pen. Either method though relies on the same thing, calipers to measure the end of the blank to the coressponding kit part. If you have some corian laying around, you can drill a 1/4" hole in it and mount that on your mandrel. Use a parting tool to make your own bushings out of the corian...again by using calipers of course. Then you can use those bushings on the rest of the kits..just be sure and not sand or chisel your corian bushings once they are made to size or they will obviously become undersized.
