Doug,
The JL code is a rim used for the space saver in the mid-size line such as Torino, LTD II, T-Bird, Montego, and Cougar through '79. The tire used for those applications is H78 x 14" like on the rim you have. This rim has been around with different part numbers, code IDs, width sizes, and ratings since first used in the '68 Mustang. This rim would fit the Mustang, but the H-78 size is a bit larger than the F-78 size specified by Ford.
The JL rim is 14 x 5 1/2" with the width measured where the bead of the tire sets inside the rim lip. The date code on these rims is first position-year, second-wheel manufacturer, third-month. The six would indicate 1976, and M would be Motorwheel Corp. For the month, you need to recheck for another letter. Ford occasionally used a 24-month calendar (leaving out the I and O) for the month codes.
The problem here is that the rim is compatible with a Mustang, but the tire is too large for a Concours level Mustang. Spacer Saver tire size is something that MCA (Mustang Club of America) would check at a judged class show. These tires, regardless of size, are also not safe to be used for any actual spare tire duty. I know some Dodge, Plymouth, and AMC vehicles also used the F-78 x 14" space saver size and struggle to find show-worthy tires. To my knowledge, no F or H78 x 14" space-saver tire is being reproduced at this time. Your tire would work for someone with a Mustang if they wanted a space saver regardless of tire size. If you get no hits here, I would try the 68-79 Fairlane-Torino site.