I have had (3) 440 and (5) 400 73-78 C Bodies and all (3) 440s car were definitely noticeably quicker that the 400 cars even though they were more loaded up with options which adds more weight. Although none of them are/were race car fast.
Wish you were closer, I would have been interested in the engine, trans, rad and everything that bolts to them along with the power window motors, harnesses and switches.
I have mineral spirits in mine. The same stuff has been in the tank for almost 30 years. I just scrape the goop off the bottom of the tank once in awhile. Stuff still works great even on the nastiest of parts , but does leave a dirty film afterwards once mostly cleaned. I then just do a final...
I got red X'd all the time on several of the Bodies sites. Never bothered me, never cared. I learned some may do it on error when hitting reply also. Hell, I have probably done it also and didn't even know it. Stuff happens. We all just need to move on....
I would think you would want to re-use the C Body tank straps over buying the new straps with the B Body 68 Coronet tank. I believe since the C Body tank was larger, the mounting points will be further apart. The B Body straps make not be long enough.