what brake booster do I have?

[64stpside]

Here's what's up with this truck.....
The booster went bad on my 64 c10 (4 wheel drum brakes). I don't think this was the original booster and bracket setup. I ordered this one from rock auto :
https://www.rockauto.com/en/moreinfo...=1351&jsn=1351
It looks nothing like what was on it and it's about 2 in narrower than the old one as well.....but rockauto says this is what's supposed to be on it....The holes in the bracket on the new booster didn't line up ( neither did the top holes of the old booster) but I thought maybe just a different design, drilled some new holes and mounted it up. The pedal is really hard to push.

Things I've checked so far:
I had air hissing from the booster when pulling the the valve off the booster when the truck is off, no hissing when pushing the pedal when the truck is running. When the truck was off, I let it roll down the driveway and it's easier to push the pedal down than when the truck is running with the booster hooked up????? Weird right.....

Unless I'm missing something, I think I should get the same booster I had on it but I don't know what it came off of. It has delco moraine stamped on it. I think this originally came off a disc/drum set up as the master cyl that was on it had a bigger reservoir in the front than the rear (I put a 4 drum mast cyl on it). When the old booster worked, the truck stopped very very well. Is the old booster a dual diaphragm? The one I got from rockauto is a single. Here's some pics