An LRB is a fine piece of workmanship! Single or double lug? You ought to check the chamber for the depth of the leade (that bit of jump before the rifling). That is the sort of rifle built to shoot a particular weight of bullet - 147, 155, 168 or 175 grain. When the M1 and M14s were still competitive in US fullbore shooting and the big service teams were tied to issue supplies, their advice was to shoot as many different lots of ammunition as possible to find the one that made their rifle sing. Keep that aside and hammer hard!
In a pre-rolled ammo situation, you should plan on buying a couple cases of what looks good and doing some testing. There are probably three case quantities of types circulating - Austrian pretty-close-to-NATO Hirtenberger (Boxer and Berdan primed, someone else will help with the particular years); US surplus Lake City NATO ball (umm? why are they selling new production ammo for cheap?); and Chinese whatever they can flog. Canadian IVI and DA issue ammunition circulates on the secondary market. IMHO, choose the DA first for ball vs IVI. It might be from the 1960s, but it started out with superb QC.
You may also encounter Brazilian CBC from the 1970s. DO NOT fire this! Recognizable by the green sealant, severe primer crimps and paper boxes that say "Reengastada". It is dangerous and unpredictable. However, remanufactured CBC in paper boxes marked as Gold Cross is very good, both because the powder has been replaced and because it will have 155gr Sierra bullets.
