When I think of pruning a muscadine I think of pruning it out of trees and power lines.
Here's my two muscadines (7,8,9? yrs old). They were carefully picked out and bought but I cannot remember their names now.

They cover that entire side of that yard (several trees) and have been cut out of the power lines.
A good old mature muscadine makes a think tangle of vine that you can lay in without fear of falling through. The old gardening books called it a bower. So you climb the tree, lay in the vine and eat to your hearts delight. As a kid that's how we did it with the wild vines (we would climb 40' in a pine tree and lay in the wild muscadine vine to eat grapes)- and that's how I do it now.

Wow! That sounds like fun!!

Should I cut off the lowest branch near the trunk and let the two V shape branch to grow ?