These are a shooter. Not mine but just came across it.
https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/19325008/remington-788-in-223#Post19325008
I was trimming with the same setup as you and when you have a lot of brass it is for sure slow. Last year I bought one of these and it is fast. Just going steady I trimmed 100 270 wsm in 17 minutes.
For an old single shot shotgun. From what I gather models 94, 220, 220A and 107 B are are the same.
Looks like this
https://www.gunpartscorp.com/products/1964420f