This is not a model site, but I have had it on my favourites for some time, and I'm sure many people have already seen it, but it should be of interest to some people doing conversions.

It is mostly related to full size quad engines, but there is quite a lot of valuable info in here (on the whole site) - suited to all two strokes.
( For those who want to use some imagination and initiative.)

http://www.macdizzy.com/cyl_primer.htm