I recently swapped the drive line from an 88 TC into my 89 Mustang. I took it out for a test drive and it sounded like the boost would come back though the air filter....kinda sounded like a BOV but I do not have a BOV.
Yeah you probably need a bov, The extra air will stop the turbo from spooling and you have to wait for the turbo to spool up again on shifts. The bov will also help the turbo to live longer!
There isnt a particular one, just find one off ebay, like a greddy unit or turbonetics or something of the like. usually you can get one for like 70-90 bucks.
look into a BPV (Bypass valve). Depending on how you have your MAF setup you'll screw with your computer by going to a BOV. When the BOV vents measured air to the atmosphere it EEC doesn't know how to compensate for it. With a BPV the air will be put back into the air stream after the MAF and maintain harmony with your computer
You can't use "any" bov, you can use any that will stay shut at idle. The key to staying closed at idle is getting one with adjustable spring pressure.
The info about running rich if you have a maf (or more specifically, a vam, which you have) is nothing more than a commonly stated rumor...there is no merit behind it if you have a properly adjusted/functioning bov.