i would use the 185's, the 4" bore won't be able to use the larger valve anyway, this way you won't have to worry about the p-v clearance and save a little cash, i don't think the 205's would gain much over the 185's imo at the rpm your looking at.
here is a discussion where i was comtemplating my options.
http://speedtalk.com/forum/viewtopic...239&highlight=
there is a cam recommendation in there also.
you'll have to check rocker geometry no matter what you use. i would go to an rpm air gap with a small open spacer if you can fit one. carb is the minimum but useable, if you go to the dual plane you will pull more vacuum and can use a bigger carb if you come across one. if you don't have lightweight flywheel/clutch that should be on the list. last, don't kill everything with a small air cleaner.
with all the above you will definitely have a different animal but i think you have the right ideas.