I have a friend that we built a circle track late model race car using a E/B-Body front suspension
( k-frame , LCA's and torsion bars). In trying various bars to get the front end to compress and return to ride height we found the Mopar bars bought at our local dealer to be junk. The problem was they wouldn't take a set and return to a consistent ride height. We then bought Firm Feel bars and that problem was solved. They returned to the ride height very consistently.( quality materials used at Firm Feel!)
Just thought I'd share this bit of acquired info , not that you might not notice this issue on a street cruiser , but if you plan on any " spirited driving" such as autocross ect I think then you would notice, that combined with the woefully inadequate spring rates offered from the factory then without a doubt I'd go with Firm Feel torsion bars!
I have no experience with the Mopar leaf springs but I've heard/read the same complaints that they sag over a short period of time. Buy quality even if it costs more, it pays in the long run!