Most manufacturers will recommend a matching valve spring to your camshaft depending on lift and duration when more than your stock springs will handle. Some machining may even be required in some cases as well.
Usually two totally different style cages and sometimes even different materials of tubing from a drag car to a road race car. Definitely, check with the rules of your local sanctioning body of whichever racing you plan on doing.
Just slip your stock tip into the larger exhaust pipe you want to use, Mark the tip where it snugs up inside the new pipe and cut it off where needed and remove the baffles.
I like my 2012 R/T Classic with 84,000 on it now and no issues in 13 years. Eventually, I want to buy B5 blue H.C. to go along with my blue 70. However, I do love this color blue also.
I welded a pair of old Megs megaphone style tips on one of my buddy's cars before. I just cut them back for the 2-1/2" dia pipe we needed. I never heard anyone comment that they didn't look factory. At least not from the average street crowds. Now, the true date coded, numbers matching weenies...
I deal with dozens of different people every day ordering 10's of thousands of dollars of racing parts everyday. Sometimes I just brush it off as someone may just be having a bad day. Others times I just work them over with my charm. Lol. In the end, I have to work along with them everyday and...
As mentioned above. I have a couple 440 Sixpack set ups, a 383 (short deck) Sixpack and a 340 Sixpack set up. All will take the same carbs, spacing is all the same and the aircleaner assemblies are all interchangeable. However, there are several different designs of aircleaner assemblies.