Hot Heads 340 oil pump
The chrome moly shaft simply wore out in 37,000 miles and I had to replace the pump.
The new Hot Heads pump fell apart on the way home from Louisville this August and I lost the engine (3 rods through the freshly-chromed oil pan).
The stock pump, if the body isn't scored, will work fine. However, if the pump cavity is scored or, otherwise, worn, you'll never be able to reach the maximum factory oil pressure, even with a rebuild kit, as there'll be too much oil leaking around the gears due to the worn housing to even reach the relief valve setting.
FWIW, I ran my hemis (3 different blocks, same crank, rods, heads, cam, pistons) with 25 psi (hot) for well over 200,000 miles until I swapped in the Hot Heads oil pump. I was, finally, able to drive down the road with 55 psi (hot) but the "soft" shaft that Bob Walker puts into his Melling pumps isn't up to the task. It simply wears out. .....but his wife INSISTS that they've "....never had any issues with these pumps and sell one or more pumps every day"