Hey guys,
Im looking for a frame to swap in for my whale of a Ross gran touring. Its a single speed and I have some decent parts on it that I want to put on a better frame. I'm hoping to find a decent FRAME for under $100 (more like around $50). I have two frames on my list that sort of fit my budget:

Centurion Ironman
Centurion Lemans

I know these bikes have sub- models or different versions like the Ironman Expert vs. the Ironman Master. For the Lemans there is the Lemans RS vs the Lemans 12. Do these "sub-models" share the same frame? I assume that there are some differences in components, but if I already have parts, I could just opt to get the cheaper one (if they share the same frame) right?
Thanks in advance.

If anyone wants to make any suggestions to add to the list please do so! I'm just looking for a decent lighter weight frame that handles and responds. if It has 27 inch wheels that is a BIG plus! Sorry if this post is a little much
Thanks a lot!