I recently looked into this myself. Per the information on the Chainsaw Collectors Corner you could originally buy an 041 or 041 AV with up to a 25" bar, and an 041 Super with a 28" bar. So, I would say it's safe to assume those are safe lengths. If you're not in a hurry and don't plan to completely bury the extent of the bar you could probably go a little longer - especially if you're willing to go to a larger pitch.
Of course you could also go with a longer bar than recommended and outfit it with either a half- or full-skip chain.
There are many other more knowledgeable folks here who I'm sure will correct me though...
I ran mine with a 18, and I think a 20 would be just about right for that 60 cc motor.
I would want a little more engine for a 24". The 041 is torquey tho, it might pull it.