Ok, I've dug up some of the optional gauges that were installed just left of the ashtray on 64-66 trucks which consist of the voltmeter and oil pressure gauges. Also I'm including a pic of oil pressure gauge used on large series trucks that's integral with the cluster, I've also tried to fit it into the housing of the optional dash mounted oil pressure gauge and it could be made to work, best thing about it the numerals match the cluster gauges
