Jack, (and anyone else)
You should be aware of the Charles Dockstader valve gear programs which are freeware and easily found on the web. One thing to know about them however is that these aren't primary "design" programs, they are a proofing programs. You design your valve gear (or find a previous design) and plug its parameters into Dockstader and the program will show you how the gear is work and from that allows you to make fine adjustements to maximize your gear. It is not as easy as it sounds, at least for me. A Walshearts gear, for instance, done from scratch has around 57 variables (IIRC) to be determined before the gear can be proofed.