you sure you have the code correct, 4fb1 seems to be a 1.8 featured in the gemini
if its a 3.9 i would think its a 4bd1, maybe the identification is a bit mucky.
engine is pretty popular in australia where it was available from the factory in stage 1's and 110's. also used in the perentie.
is it turbo or non turbo? in the uk i think the engine was only found in small isuzu trucks.
there's even a bit of forum for them
http://www.4btswaps.com/forum/forumdisplay.php?f=16 no idea how much its worth really, suppose it depends on condition etc. i've seen them go on ebay for a reaosnable sum and if you have the adaptor and bos, that's half the battle for someone.