Each carb has a return spring on the linkage shaft, right behind the linkage rod. These springs are wound so tight (PO setup) that my accelerator is too stiff to push down. I have to push hard, and suddenly it's down too far. I can't feather the gas pedal.

CB Crossbar is lubed and free. When the linkage to the carbs is disconnected, the crossbar / cable float free and the gas pedal is slick smooth. Double checked, and not across the clutch cable.

Can these springs be unwound some or removed and a return spring put on the crossbar??

It's good to have some sort of spring right on the carb. That way if the linkage breaks or your main return spring breaks, the carbs will shut down. I have a spring on the linkage as well as fairly light weight springs on the carbs themselves. But yeah, use whatever springs makes you happy so long as the carbs go closed quickly. Not too stiff or you'll break the throttle cable.

Be absolutely sure that the return springs are in fact overwound before messing with them or you could create a potential deadly situation. It's really unlikely that they are overwound.
Keep in mind that the CB hiem joints suck, they do not rotate freely and will cause difficult linkage movement. Also, if you are using them, the CB throttle shaft arms are too short which causes two problems. First, short arms make turning the throttle shafts more difficult than a longer arm and, second, the short arms make for an abrupt throttle response.
Make sure the hiem joints spin freely in their sockets and if you can possibly find some, look for longer throttle shaft arms. Dell shafts are slightly smaller than Weber shafts, so finding arms that will fit nice and snug is a very tall order. Art at ACE VW has stainless arms a bit longer than the CB arms, but they are loose on Dells and will have to be peened around the shaft knockout to get them to fit snugly. It's a trial and error process to get them to work, but so is the whole carb thing. Good Luck