ID THIS BLOCK

The 'R' is Std. Passenger Car unit, 'Regular', which earlier in the series meant Regular Fuel. The 'E' stamped at the end ID's the block as a cast-crank unit, no matter the casting#.... very important when it is the 1st run at the switchover period in '76.
The cast block, rods, crank, & bearings are all different from forged crank units. The dampeners were changed, but I don't think for being 'cast', since all inline 6's are inherently balanced by design.
The hydraulics can be swapped out, tappets,pushrods,rockers, & cam. I'm not 100%, but I believe Shane...Member @dart19666 tight-lashed solids on a hydraulic cam, You could contact Oregon Cam Grinders & have a set of solids resurfaced to use on the Hyd. cam.
Later blocks all using hydraulic tappets/system have block casting#'s of either '330' or '530'.