Help with 340 compression + cam change

Mmmmm.... I vote NO on reusing the worn 273 rockers. LOL Makes no sense to 'ruin' this big change with poor parts!

IMHO you are definitely on the right track. Quite a change in the cam there, going from 214 to 235 @ .050". For sure ought to make it stronger up top. And the lower 'advertised' (measured at .015" or .020" lobe lift for a solid) ought to boost the low RPM performance; it won't be a barn burner at low rpm but for sure better. This cam ought to be quite different than that old slow ramp thing you had!

Make sure you look over the seals and retainers when you get the springs set up, and make sure you have adequate clearance between retainers and guides/seals; you lift is going up quite a bit.

Also, check piston to valve clearances..... put a pair of light hardware store springs on one cylinder (#1 is easiest) with everything installed and cam timed and lash set up. Slowly rotate the engine so you go through the overlap cycle on that cylinder, and starting at 30-40 degrees before that cylinder's TDC, and continuing to 30-40 degrees after TDC, stop every 3-5 degrees, and manually push down on each valve to see how much further they have to travel to stop on the piston. That extra travel is the PV clearance you have at each measurement point. Make sure it is adequate. It very probably will be, but with the light increase, and the higher RPM capability of this cam don't take a chance.

Be thorough on the break-in; these steeper ramps are going to put more dynamic loading on the lifter-lobe contact.

Sounds like a good move, IMHO.... hope you enjoy it, and are happy with the change.