MH 452’s can also have the extra coolant holes...... and those usually use tapered seat plugs.
I’ve had a few sets of 213’s here........ they didn’t have the extra coolant holes. They looked like 346’s...... but flowed a little less(which kinda surprised me).
Ootb, 346’s, 902’s, 452’s....... all flow basically the same.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads