Intermediate Shaft Question

This is my first small block Mopar build and I am not sure if I need to get the heavy duty intermediate shaft or can I reuse the one that was in it? I am building a 340 for my son's 1967 dodge dart. The engine has the J heads and a Lunati 10200703 cam. The operating range is supposed to be from 1800-6200 RPMs. My machine shop seems to think I do not need it and couldn't get one from his parts supplier. The shaft that was in the engine looks ok but does not have the pinned gear. Has anybody ever had one of these break or come apart? How about any tips for dropping it in and getting everything to line up correctly?

Thanks. I appreciate any info I can get.