1948gmcpu,
first off, welcome to the vcca chat...while you currently have a nice gmc pickup project, I can see from your profile that you're a lover of '50-'70s chevrolets & camaro's, so in that regard, you've come to the right place...this chat is set up by and for those dedicated to the restoration of chevrolets...
some of the other contributors here are really knowledgeable about all the old electricals, but I find cranking speed of six-volt systems is slower & is more dependent upon battery, cable, & starter condition, & proper connections than modern twelve-volt starters...there's less margin for error...
you might find the parts you need from a number of vendors often discussed here...I like to patronize the filling station, american classic truck parts, chev's of the forties, obsolete chevy parts, jim carter's antique truck, & hampton coach...
and, if you join the vcca, you'll receive a monthly magazine containing information about the club events & stories & pictures of the members' treasured chevrolets...each month there's a rush to see what parts are newly available in the classified ad section, a great way to find those hard-to-find parts...also, many skilled craftsmen, mostly also vcca members, list their services, such as speedometer & gauge rebuilding...
so, welcome...hope you get the info you need here and best of luck with your project...

epi