Alternator and Muffler Questions

Been a little while since I've posted, but I'm sure you're all as helpful as before. I'll try to be as detailed as possible. My car is a 1980 Caprice Classic, V8 5.0 (engine H)

I think I may be having trouble with my alternator. Whenever I have my lights on (my high beams especially), they're a bit dim if I'm not accelerating. The same happens with my dome and dashboard lights. I've been told that it's probably my alternator. Would it be? If so, about how hard is it to replace one?

Next question is, how do I determine the size for the inlet and outlet for my muffler? I have the OEM one on there now, which has rusted away for the most part.

Thanks in advance ^_^.

It's 2-1/4 in and 2 out on the muffler for an '80 LG4.

On the alternator - this could be normal behavior. Check to make sure the engine is idling at least 600RPM in drive with the brakes on. Also, you can check to ensure the drive belt is in good condition, not glazed, and at the proper tension (1/2" belt deflection on the longest stretch).

In addition to those items, inspect/clean/tighten the battery connections, ground straps and cables, starter main power connections, and power output stud at the alternator.

If the drive belt is glazed, you might also want to polish the alternator sheave with 220-400 sandpaper to break that glazing, too.