From what I've gathered, it seems like you have a strange bolt pattern on your current flywheel. We've sold tons of these Ram clutches and haven't had any issues with mounting to the factory flywheels. It makes me think your flywheel is from another year Mustang like a 05-10 or another Ford causing the current clutch to not line up.
Either way, I just wanted straighten some info out and make things right for you. We DO have a flywheel that will fit your current 88951HDX clutch. I'm sorry for any confusion you had over the phone, but the CS Rep was definitely off on his specs. We have the RAM Billet Steel Flywheel
for the 6bolt crank and a 11" clutch for $309.99 that will work with your Mustang. Since you've gone through so much hassle, I'd be happy to hook you up with this RAM Billet Steel clutch for $285.00. This should take some of the edge off the cost and will definitely end your flywheel problems!
Shoot me a PM if you're interested and will get things rolling ASAP!