Are you sure you have the correct shaft Milidon makes a longer one for there pump with the external line, are we talking RB, B, or A. Did you check them side by side with the O.E. one?
It's the right one, sorry forgot to mention that it a small block, aftermarket block. It's for high volume pumps it's the one from mancini:
Fits: Small Block 273-360
For Use with High Volume Oil Pump: Yes
Hardened Shaft: Yes
Sleeve Included: No
Drive Gear Included: Yes
Gear Material: Bronze
Quantity: Sold individually.
Notes: Bronze drive gear, designed for use with mechanical roller camshaft.
These oil pump driveshafts are CNC-machined from 4130 chromoly and are centerless-ground to avoid stress risers. These race-proven shafts eclipse breakage-prone stock units that frequently fail when used with high-volume oil systems, heavy racing oil, or high-rpm applications. The ends are induction heat-treated to reduce wear.