Tranny would swap too.
The exterior and the interior won't swap between the 68 and 69 since they went through a complete restyling and to a larger body in 69. The dash, doors, and rear interior trim is completely different. The exterior body panels and chrome are different too. The windshields won't even swap since they went to glue in glass in 69 and did away with the gasket on the pinch weld they had all the earlier years.
I've slowly been watching what 69 fastbacks (and converts) have been fetching the past few years as I'm hoping for one for my next project car. The prices have gone up a bit but 6k for a car missing major components is pretty pricey. If this guy is picking them up it sounds like he's just flipping them. I wouldn't be surprised if he's getting them between 2k and 4k and then reselling them at 3.5k and 6k. He's in his right to do that and if he gets people to pay him for them then more power to him. I would still look at the cars, like what was mentioned, you don't know what they are yet, but if they are T, L, F, or H codes in the VIN then it's kinda high and you might find a better deal elsewhere. I have seen the 4 barrel M codes command slightly more than the 2 barrel H codes even though they are both 351s. If they are G, S, Q, R, or Z then the prices aren't bad.
I should give a legend to the motor codes if you don't know what they are:
T- 200 ci inline 6
L- 250 ci inline 6 (note: this is the only 6 cyl to get a 5 lug suspension from the factory)
F- 302 2v
G- 302 4v (this is a Boss motor and a car with this VIN is a Boss)
H- 351 2v
M- 351 4v
S- 390 4v
Q- 428 4v (this is a Cobra Jet)
R- 428 4v (this is a Cobra Jet with ram air)
Z- 429 4v (this is a Boss motor and this car is a Boss)
A Mach 1 couldn't be ordered with anything less than the 351 2v. The G and Z were only for the Boss cars.
Do you have any pics of these cars? If you can get the door tag info that would be good too plus the first half of the VIN. No need to post the complete VIN as I know some people don't like to do that. If they still have buck tags bolted near the passenger side hood hinge (for Metuchen built cars) then post that info as it will mention any major options the car has/had.