Setup for 273

Adjustable rockers on a hydro makes perfect sense: Mill the head and you can still use the same pushrods (to an extent). More accurate ratio@~1.5. The stamped are all over the place. Adjustables have more accurate geometry as you can shim them to cover the valve tips. The Isky E-4 is a solid lifter cam. The lobe profile is not meant for a hydro lifter! In the worst case the hydros will "pump" and youll start lifting the valve at a very early event as the solid would take that duration to close its lash. Also hydraulic profiles do not have these ramps, they are straight lift and seat with no variation around the back side of the cam so the lifter is static on the back side. Mechanicals have much different base profiles. Thats why Mopar has that handy diagram on where to adjust lash as its very different on various points of the base circle. E-4 is an old grind made for "10.5:1" pistons. Builders can do much better just by dropping a cam maker a call and have them custom make you a grind for your static compression ratio and induction/exhaust setup. As for heads: You can use modern "302" casting swirl port heads off a pre-magnum 318. They are closed port like the early 273 heads and have hard seats as well as being very easy to find, just check for cracks between seats.