That really doesn't look like a Pro Stock car and it would explain the lack of a fiberglass bumper and probably front end. Several A-body Pro Stocks did have chopped and channeled front clips.

Several Mopar racers did run in some sportsman classes in the mid '70's when, I believe, Chrysler pulled back on the Pro Stock program because of the unfair weight breaks.
Could it be a Super Modified car? (i.e.: B/SM)