She is certainly worthy of a 440. Needless to say; It will become a different car all together, you will know what I mean the first time you drive it with a 440 in it. It's not just the extra power!
I owned a Challenger with a slant 6 for about 10 years and drove it to work everyday, never got a ticket and it was very good on gas, I take it you have other plans! LOL.
Are you going to swap the K frame or use conversion mounts? if you use conversion mounts it will be easier to go back to original, you probably never will though. I wonder how many slant cars still have 6cyl engines not many I bet.
Ok, So engine is complete and I finished building my engine test stand. 6 is out, 3 speed out. New K frame in and all new STOCK big block suspension. Can't wait to get her home and put in the power brake upgrade. I still need to wire the engine stand, but should be finished this week and can see how she runs.