On 2 of my trucks, im using the old 6v. starter with a 12v. system. No probs at all,it just spins a little faster making for easy starts. Theyve both been that way for at least 10 years.
As Stuart said,,"dont get lost in the techno stuff",,it pretty much doesnt get any simpler than these ol trucks.
And......Welcome to Stovebolt. Stick around,,you'll learn alot.