On mine I had to loosen the spring screws a little to get it in.
On the Busch C I have, there were washers that could be added under the spring screws, to give it more room for the roll backs (adapt-a-roll). You might try adding some, even if it meant using slightly longer screws. If you take one out and bring it to a good, old-fashioned hardware store, they may be able to give you longer versions with the same thread.

I may have been leading a sheltered life, but I've not seen a Pacemaker with a spring back. I thought they only came with the Graflock, like this pamphlet shows. Mine has one.