I’m going to attempt to build the Titan III C based on Estes Titan III E which used BT 60 tube for the main frame and solid boosters. I’ll be modifying the construction plans using BT 70 tubes and using a different method for inserting the fin tubes into the boosters. Estes Titan used BT 60 for the main tubes and BT 5 tubes for the catalyst tubes. Fortunately up scaling to BT 70 tubes the BT 20 fits the scale for the cat tubes. I’ll use BT 20 tubes for the clear fin support tubes using a tight fit on 3 1/8” plywood centering rings with a bulkhead at the top. Since I don’t have a lath or 3D printer I’ll be using card stock for all the nose ones with appropriately sized wood and plastic spheres for the top of the cones. All centering rings, bulkheads, couplers and exhaust nozzles will be made in house. Motor mount will be able to use D and E size motors. Finishing will be a challenge.