before you swap alt,get one of the newer solid state elect voltage regulators to replace the old points type you have with the round back alt with one feild wire

this will help the dim lights at idle and works way better than the points style VR

best 12$ upgrade I did to the 68Dart I had

you can run a square back alt by grounding the 2nd feild wire and hook the other up for an up grade, the one from the truck should bolt right in place of yours

you can use an external regulater denso 120 amp(late 80s cars/trucks/vans) on stock non a/c pullys,has the double grooved belt pully on it and works on the stock external VR for a good upgrade

i have one on my 440 in the sig pic on stock brackets,you just crimp on eyeloops for the 2 feild wires and bolt it on

IMHO,I would do the 12$ replacement VR first and see if that fixes it enuff for you,before changing the stock alt for another


x2 on a timeing light and vac gauge to start tuneing on the carb,all 3 work together to dial it in

good luck