Could be all over the place - if that's a 428 CJ the engine could be worth that for someone wanting to put it back in it's original car...or if the guy is wrong and it's a '68 it could be worth a lot more.
If it's just your basic FE drop in to a 67 coupe, the price is probably about right depending on the condition of each.
Prolly want to take someone that can decode the data plate and engine codes along with you if you go look.
There were some Shelby coupes made, but I don't have knowledge about them or any info handy unfortunately.
After a little digging, here's what I came up with:
There were 2 official Shelby coupes made, one in '67 and one in '68. The '67 was called "Lil' Red" and ended up getting cruished notnice and the '68 was "Lil' Green Hornet" or something. That coupe is still alive and kickin'.
The easiest way to ID a 428 is look at the flywheel or flexplate. There will be a counterweight on it. Only drawback is the 410's also have the counterweight too. (390 block/428 crank = 410) CJ heads are easy to id using the casting numbers between the center spark plugs. The engine code in the VIN will be useless, as already been pointed out, no 428's in 67 Stangs. Could be a 390 car though, 5th digit will be a "S". 68's also had a 390 2 bbl option, don't recall the letter code though.
The easiest way to ID a 428 is look at the flywheel or flexplate. There will be a counterweight on it. Only drawback is the 410's also have the counterweight too. (390 block/428 crank = 410) CJ heads are easy to id using the casting numbers between the center spark plugs. The engine code in the VIN will be useless, as already been pointed out, no 428's in 67 Stangs. Could be a 390 car though, 5th digit will be a "S". 68's also had a 390 2 bbl option, don't recall the letter code though.