I've been scaremongered by some older locals about my crank bearing causing my engine to seize up.
two main issues with the crank play
1. end float
2. worn timing side bush
Quick way to check both (well not that quick)
1. End float - remove the primary chain case and the shock absorber arrangement and sprocket from the crank, pull the crank back and forth looking for movement, initial set up is max of 3 thou, obviously with use this may have increased a little.
2. timing side bush - remove the timing side cover, probably best to remove the oil pump, then look for lift on the crank pinion.
Many of these old bikes are travelling along quite happily with a bit of play and a bit of end play, I wouldn't panic unduly, ONOH your probably not going to be happy now until you've satisfied yourself of the old girls condition, if it aint banging to much enjoy it for the time being