Best way to flush engine after rocker arm failure?

The rocker shaft bolt holes in the SB TF are pretty deep.
Deeper than what you’d get for thread engagement from a typical bolt or stud.
The hole is about 1-5/8” deep, and I’d want to have the fastener get as far down into that material as possible(to help support the stand).
I’d get some grade 8 threaded rod and cut it into pieces the correct length to end up with a couple of threads showing on top, above the hardened washer and grade 8 nut, after having it basically bottomed out in the hole.

One of my least favorite things about the “bolt on” aftermarket heads for the SB Mopar, when using a cam that requires fairly stout springs are the 5/16” rocker shaft attaching bolts.