I'm building a scratch Jupiter C using a 66 mm tube for the booster. I'm using Peter's book for my scale dims. From the original Estes kit with the 2 inch ST-20 tube, I'll need to increase the fin dimensions by 29.4%. 24mm motor mount is complete and working on the ply fins now. Hope it will not be too heavy to fly on D12-3's. 2-3 hundred feet is fine for me. Doing my calculations, the upper stage housing should be 38mm in diameter if my maf is correct. I think I'll just use a BT-55 or 33mm tube for that. Any suggestions what to use for the actual satellite or corrections I should know about?