[elmariachi]

There could be as much as a $10k swing on these engines, depending on several variables, the reputation and knowledge of the builder being one of the biggest. You need a lot more details for an accurate estimate, such as production or service block? True side oiler or drilled? Previous marine engine? Cylinders bored? Line bored? Sonic tested? Crank magnafluxed? What brand of rockers? Which heads (a big one)? Which carbs? Compression (able to run nasty pump gas)? Etc etc etc.

Warning, lots of scammers scarf up junk piece-meal off eBay, package it all together and try and say they have an "awesome race-built 427 side oiler for Cobra..." Don't be fooled. Takes a lot more than the words "side oiler" to be of any value.