Voltimiter Yes there is ~ I'm not sure who makes it tho' , maybe Randy Rundle @ 5Th. Avenue Auto Parts ? . Or , just add an under dash one like I did , it's near my old timey engine vacuum gauge .
There is a shop that advertises that they convert ammeters to voltmeter called Bob's Speedometers. Here's a link to their website. www.bobsspeedometer.com You might visit with them and see what they might be able to do for you. I've never used them so I can't vouch for them or their work, so caveat emptor!