My clone o' t' estes #1379 Mach-2 kit available 1982-1984 which was me first "D" powered rocket as a kid back in t' early mid 80's. Well, blow me down! I used a Estes E/D engine mount t' have t' option o' usin' either a E9-6 or a D12-5 with a spacer. If I'm darin' I can also use a F24W, but OpenRocket had it at 2100'! I like t' get me rockets back though but its nice knowin' I can use that engine if t' need arises.