I have an Estes #2157 that I got about 4 years ago in a trade for some Eggtimers. The plan is to make it a two stager with flip-out fins on the top stage, with five 24mm motors on the bottom and one 29mm up top. The way that it's constructed actually makes doing any two stage conversion relatively easy... if you've done one before. Like kuririn says, you'd want to use modern electronics, if for no other reason than that they have safety features built in to prevent unintended ignitions.