Stock Magnum Intermediate Shaft w/Melling M72 Oil Pump?

So I'm buttoning up a 5.9 Magnum rebuild project and having trouble installing the stock intermediate shaft that came out of this engine. I replaced the original oil pump with a Melling M72 which I thought was a standard volume stock replacement. However, now when I try to install the intermediate shaft, it doesn't want to drop down to engage the camshaft gear.

I used my priming tool to measure the distance when it is seated in the oil pump to the intermediate shaft bushing. That measurement is about 1/2" shorter than the original intermediate shaft out of this engine. The measurement is 7".

What is the correct intermediate shaft for this application ? Thanks, appreciate any help in advance. This forum has been a great resource through this project.

Dirk