$350 for that Mercian??? You have got to be kidding?? I'll ask Bubba if he can take a look at the specs about what would need to be replaced to make it cassett-compatible.
If you can deal with the bar ends (friction shifting), my inital guess is wheels you'd loose the Phil Wood hubs
) and a new chain. As long as the chain width worked for the crank you'd probably be set and could trust that repairs could be easily dealt with.
RSX cranks, 175 length - aren't these the old Shimano touring cranks so the chainrings should be small? Jobob? Cindy, when you email ask about the chainring sizes.
I'll email Bubba and see if he has time to take a look.
Frends know gud humors when dey is hear it. ~ Da Crockydiles of ZZE.