The original WW&F used 30-35-lb. rail on the old W&Q (Wiscasset to Albion) and 56-lb. rail on the Winslow Branch (Weeks Mills to Winslow). This is according to Maine Railroad Commissioners' inspection reports, as well as pieces of surviving rail. I don't think the original railroad ever used 25-lb. rail, though elsewhere in Maine the Kennebec Central RR was all 25-lb. rail, and even the SR&RL was reported to have had a little bit of 25-lb. on sidings and logging spurs as late as the 1920s, some of which could conceivably have come from the Billerica & Bedford. (The SR&RL trunk line from Farmington to Phillips was upgraded to 56-lb at the turn of the century.)
It should be noted that the 25-lb rail in place today on some tracks in the Sheepscot yard is original Kennebec Central rail, so while lighter than anything used on the original WW&F it is nonetheless historically significant.
-Philip Marshall