I doubt unless a more modern design alternator that you'd "top" it off. Similar problems to many 12v trickle chargers that never bump up. It requires your alternator to push it to full.
Gauges and smaller light bulbs may not like the extra voltage. I think a better choice would be a dual post battery with 16v to starter and ignition (if aftermarket type) and 12v to accessories. Headlights should work well on 12v if properly relayed to battery with adequate gauge wire. Don't many suggest that the AMP gauge is one of the culprits in our Mustangs?
69 351 TKO Sport Roof
70 557 PG Mach I
67 347 TKO Coupe open track car
67 289 C4 Coupe cruiser
69 460 SCJ TKO convertible
94 351 TKO NASA Mustang
911 RS Tribute, 964 widebody, 993 twin turbo,73 911 rally, 70 914-8, 72 MGB, 67 MGBGT sbf, 67 XKE, 69 Buick GS, 02 Harley F150