Amps are amps but having more accesories draws more of them, you can overload an old ammeter. If so you're better off not using it at all. a voltage gauge is a better way to monitor battery and charging system.
The link above and again here addresses the ammeter to voltage swap
http://www.speedometershop.com/enc-pag.htm

Here's an idea for updating the speedometer, and the second post there is a link to yet another way to do it.
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=847088

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-