Years ago, I reinforced my K-member with a plate that wrapped around that same mount. So it's very close to rubbing on my car. But thats with that plate.
I though that was very close for that 73-76 K-member. It's a tight fit.
I'll try to measure the difference between a NOS 318 left mount and an original 340 68-72 biscuit style mount over the weekend. Maybe adding a 1/4" spacers on that side?? But I can understand if you don't want to do that.
I'll pass this info on to Milodon.