The short answer is... there is no one single trap that will serve for both beaver and muskrats. I would set the bigger hardware on the slides for beaver and trap the muskrats elsewhere.
But here's one piece of advice. Don't "construct" any sets for muskrats. If beaver see fresh diggings or fresh disturbances along the bank, or smell lure, they will come to investigate. You won't be able to hold them in muskrats traps, and at worst they could run off with your equipment. Look for muskrat dens or natural little alcoves where the rats hang out. A good beaver proof set is a muskrat toilet. Look for rocks or logs on which the muskrats are depositing their droppings and set traps there.
Endeavor to persevere.