Now don't get me wrong the mod motors, at least 4.6, is a proven design. They'll go 300K+ in taxis and perform well enough for a point A to B passenger car. Overhead cam and all the associated complexity wouldn't be my personal choice, but in that application they do fine. In a truck or a towboat, no way. I recall Chevy did a blind test of a SBC based pushrod engine and a new overhead cam engine in Corvettes some years ago. Identical cars otherwise and had many people drive them and compare which felt faster and which they liked better. Despite being similar displacement and HP, the pushrod engine felt like it had a lot more low end grunt and thus more powerful to the test drivers, hence why Chevy's bread and butter is still a SBC based pushrod V8.

Overhead cams add lots of complexity and are best suited to higher RPM. Go back to the Ford 427 SOHC. It was a screamer, capable of running 7500+ RPM all day. Very expensive complex compared to a regular FE. The high RPM advantage comes from eliminating pushrods and lifters. That's a lot of weight that accelerates, decellerates and changes direction quickly. With an overhead cam you don't have as much weight on the other side of the spring so less valve spring pressure is required and hence the valves don't get abused as hard as with pushrods and lifters. Sustained high RPM is the only reason to go OHC, and in an application that requires high torque across a broad RPM range an OHC engine just seems like a square peg/round hole scenario to me.