And if you're a rookie, you might have to come to a stop to start all over again. I cut my teeth split shifting a 68 Pete with dual 4 speeds and worn out linkage. Had to bring that rig to a stop more than once when I got both boxes hung in neutral.

What you are trying to do is match the speed of the output gears to the input gears. One method is double clutching, as just described, best for beginners.

The other is shifting without the clutch, tougher to learn, but faster to shift. You back off the throttle slightly to get out of gear, then lower the engine rpm to match the gear you're grabbing next. When you get the hang of it you can slide into the next gear. Downshifting isn't as easy.

Fred
52 3600
69 C-10