My clone of the estes #1379 Mach-2 kit available 1982-1984 which was my first "D" powered rocket as a kid back in the early mid 80's. I used a Estes E/D engine mount to have the option of using either a E9-6 or a D12-5 with a spacer. If I'm daring I can also use a F24W, but OpenRocket had it at 2100'! I like to get my rockets back though but its nice knowing I can use that engine if the need arises.