It's a CC-16.
This looks like it was a Canadian market machine, which is why the bill acceptor opening looks kind of wonky. American machines have a smaller BV opening. I forget if the guide connects to the door or the BV. If it's the door, you're out of luck unless you can find the American style panel. If it's the BV, check rudysdeals.com, they have the guide.
If it's giving 5c credits for a $1 bill, you'll need a 25c clear chip to fix that (rudysdeals again).
For not accepting $50s or $100s, it could be the amount of credits would exceed the credit limit set, or that the BV hasn't been updated to accept the new bills and needs an update.