For the slower lightweight classics like a Kwik Fli, etc. the Enya 60, Veco/K&B 61 and Webra Blackhead. If you want a slower classic go fast and you have retracts the RJL 61 (the old Kraft engine) and the Irvine 61 (Irvine loves a pipe). For classics that preform best at high speed like the Tiporare, Blue Angel and Speeda my choice is the piped OS 61SF-P ABC powerhouse. The Veco/K&B 61 (Twister version) and RJL 61 are available new from http://www.mecoa.com/. All the others are in good supply NIB from that site where you bid on stuff or the RCU Market Place. Used engines that have been run even slightly and then sit for years may need new bearings so keep that in mind. I’ve bought a few used but they did require a bit of work even though they were very clean looking.

Lots of engines available that are period correct and that is one of the cool things about the classics.