found this interesting article THE HISTORY OF MOUNTAIN MOTOR PRO STOCK
The article says ...
“In those early days it was really hard to find the blocks, so you did whatever you could to make the engines bigger,” Leonard said. “The camshafts – you’d put more stroke into it and your rods would hit the camshafts. It was a headache.”
http://www.competitionplus.com/drag-...otor-pro-stock