On inspection, the shafts were not seized, in fact, I pulled them out with my fingers!
Installed new springs on Rich's advice ( as per FAQ ) Will report back on that.
Suspension is cleaned and ready for some fresh paint.
Can't believe the luck I have had on the two sleds I have taken the driveshafts out of.
In both cases, the lower sprocket came off without a puller, just threaded a 5/16 bolt into one of the holes, and wriggled it off

Shaft looks good, ( as it should as sled has <500 miles on it ) But the speedo drive key looked like a pretzel ( though it worked ) and I found a piece of cleat wedged up in the top of the tunnel
:o
New Kimpex track is ready for installation, will put fresh bearings on the driveshaft while I'm in there.