Stock mechanical pump?
The Hughes eccentric I would view as temporary ( one season?) as I REALLY want to cam this thing!!
But I told Dany, even the stock cammed Magnum is a big HP improvement over the 2bbl 273...
I did put a Holley mechanical pump on "just in case", but it wasn't necessary. It didn't change a thing. I've had so many combination of "very mild" street cars that easily did over 100 mph in the 1/4, often they were swapped slant six cars still running the factory slant six fuel lines.
Yes, a stock magnum would be a huge gain over a 273 2bbl. In fact, a stock LA 318 2bbl would be a nice gain. I've gone 15.9's with a bone stock LA318 2bbl, stock manifolds, 2.94 gears in a b-body.