I've heard there's an 88 GT for sale on the Southwest side of Atlanta (Fayetteville) that has a 3.4 in it. The engine was installed a year or so ago. The owner says it has some slight cosmetic damage to the nose from a deer strike and it needs a right front brake caliper. Other than the brake caliper, it's a drivable car. I'm told it's for cheaper than dirt. As a parts car it's worth more than I'm told he's asking for it.
Check with Ashby Arnette who did the install and sold the car. Ashby isn't the owner, but the owner advised him it was for sale. Contact him at adfieros@aol.com