351c header fitting issue

I've got a 69 Mustang coupe and have been trying to get a set of Hedman headers to fit. The car had a unknown brand on it when I bought it 6 years ago but they are all dented and rusted, but fit great. My exhaust has been hooked up to these for 3 years. Now that the car is totaled striped down for paint, I'd like to get the new headers in. I have verified that I have the correct Hedmans for a 69 coupe with a 351c 2V. The fit issue is at the collector on the driver side only. It is virtually right against the floorpan, not including he flange. The passenger side has enough clearance. I have the correct motor mounts for a coupe...it did have the convertible mounts. I believe there is only one trans mount for a C4. Raising the motor 1" above the engine mounts gives me about 1/4" clearance back at the collector, so that's not the answer. Assuming Hedman builds these in a jig.

Are there different frame mounts? Since this 351c ( which is a 72...don't know if from a Mustang or ? ) was in the car when i bought it, I have no idea what parts came from what car/year.
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I don't know if it is a help or not, but I just installed Dynomax Blackjack Headers on my 72 Coupe, 351C-2v. The only issue I had was the need to dent the primary from the #8 cylender to clear the power steering gear. There was plenty of clearance everywhere else.
Did you buy to fit a 70 mustang with 351C 2V? If you bought for a 72 that may be the problem. I have Hooker Comp headers for a 4V engine and only have some interference with the clutch rod and the steering arm which was taken care of with some slight denting of the tubes. I'm using 69 351W engine mounts. My understanding is 302, 351W & 351C all use the same engine mount.