well just got my boyds thumbhole and its to say the least, awesome O_O. the feel and structure of it allow quick mobility and easy sighting capability. the thumb hole fits perfect. my father who hates them has stated he likes this one very much. it free floats the rifle well and it needed NO modifications.
now if you read boyds stock it states its for a round receiver 91/30 most people buy and mod for a variation of the rifle.
either that or my mosin is still another weird trait in actually fitting.
i also did work to repair my barrel (which had treated rust damage but looked horrid) i used jb weld and sanded it down a day later till its flush. i then applied "high heat header paint" same as for my vw beetle. its a matt black and it was the same color as the paint already on rifle and can take high heat.
so if you have issues with your mosin i recommend this treatment so far.
oh i also found a 91/30 muzzel break at
http://www.milsurpstuff.com/proddetail.asp?prod=MP9130
no clue how it performs but was happy to finally find one