There is a member who has a pedal set up out of an F into a 5th. I think there is a floor too. Can't remember who it was, but I think it was his fathers.
Another member here was adapting a set of pedals from a first gen Dakota. Not a bolt in install and he was going to cover it step by step until his job sent him traveling.
I converted my '87 Fifth using F body components. Most of it is drop in. Issues encountered were small and easy to overcome - relocate high beam switch to floor and fabricate a "Z" bar ball stud pivot that attaches to the bellhousing. Take your time - you will enjoy your M much more.