Ask the lab to do the print "as is", without any cropping. This will produce a print roughly 4 x 5.33", or a 4x6" with white borders on the sides. Simply use a paper trimmer to trim off the borders. Saves you a lot of hassle. And who says photos has to be 4x6"
I don't know what other labs call it, but Colour Lab calls this format "DI(gital)". Slips into 4R albums nicely too.
No, 4R is 4 x 6". By printing in the special format, you end up with 4 x 5.33". Not exactly 4R, but it doesn't really mattter- you can still slip it into 4R albums.