walk around a few junkyards and pop the hoods of early 80's LeSabres... i'm sure you'll find a few low mileage granny driven cars with the motors still there, and if you can convince the yard owner that it's "just another 231", you could probably get the whole motor pretty cheap.
if i'm not mistaken (and i very well could be) a sure fire way to tell a stock 4.1 from a 231 of the same year (if the emissions decal is missing for some reason)is to look for the 4 barrel quadrajet carb instead of the 2 barrel "half a quadrajet" the 231's got.