The cost of switching from an R to a B would exceed the additional cost of operating, maintaining or even upgrading the R to an R+. Several shops in the US do B to R swaps.
Assuming identical aircraft with identical times, most would prefer the R and might actually pay a little more. As a former owner of an overhaul shop, I would prefer the B but would not be afraid of the R. I would however tell the seller of the aircraft that since it did not have an R, I need an additional discount.
