Thanks for the input lumberjack

The manual calls them tapered dowels. Locking cones works as well for me.

Still working on them. PB Blaster and brake fluid as penetrating oil and rust busters. Then hammer around the rim, and let it sit some more. That's going to take who knows how long. It's a 1970 machine, I've owned it since 1999, possible the wheel's never been off. I do have pneumatic hammers. Use them on the rim same as the sledge? Maybe a short stroke tool? Hoping to vibrate the oil into the rust mass? I'll give that a try.

Meanwhile, I think I'm going to cut the line to the bad cylinder, cap it with a bleeder valve, and try to get the system up with only one wheel online. Picked up the bleeder assembly Wednesday, Thanksgiving yesterday, going to give it a go tomorrow. Won't work at any speed. Have to take it slow, but I mostly use the truck in a 20' x 20' area. One brake should do until I can get the other broken loose.
Wish me luck