Six years ago, Vince Suddard, a race car driver and part time builder, took a similar M491 and backdated it to a long hood RSR circa 1973. The car was fully sorted by him with a transplant of a 3.6 varioram motor, but many of the details of the early RSR were put onto the car, including rear-seat delete, radio-delete, a/c delete, and even the door handles were changed. The sunroof was deleted, too. The car was amazing, and he traded me for my stock 2005 GT3 plus some cash about 3 years ago. I loved the car for two years. Over time, the values of the p-cars were climbing and hindsight says the M491 option should have been spared the knife, but Vince felt that since the fenders were virtually identical to the 1973 RSR, it would be a good project. The car is onto a new owner who I understand is loving it just as much. Here are a couple of photos of the end result:
Good Luck With Your Project!