360 Starter Problems

I’m trying to wrap up swapping a junkyard 318 for a ‘72 J head 360 and I’ve ran into problems trying to start it and finish up this project. I left the stock 727 trans in the car with stock converter but I bought a B&M weighted converter,BMM-10236, with a summit brand weighted balancer. I first installed the starter from the 318 and when I hit the ignition the starter would spin at what sounded like a million miles an hour. I figured the solenoid wasn’t firing so I tried hitting the solenoid a few times and it didn’t change anything. After some more hitting it sounded like the solenoid was firing but not spinning. I work part time and a full time student so my dad pulled that old starter for me and bench tested it and found out it wasn’t working. I bought a remanned starter from O’Reillys and got it all installed and buttoned up but got the same results. Hit the key and it just spins. Hitting the starter does nothing no matter how much I do and I’m out of ideas. So just looking for help and knowledge cause I’m out of ideas and I’d rather not have to pay a shop to figure it out for me but that’s about where I’m at. Thank you in advance.