Ford man with 65 GMC needs sage advice

[I1502]

Hi Folks...I'm in the process of buying a '65 I1502 (3/4 ton long bed, floor shift 4-speed) and I assumed that the orange small block V-8 (ramhorn manifolds, 2 BBL) was the original engine but it seems that this came with a straight six . I'm a veteran old car guy (Fords, Studebakers) and can usually spot any "butcher" work, but I'm not as yet familiar with these trucks. The installation must have been done years ago. The wavy round fan shroud looks factory, and everything seems to be all stock. Was this an easy "bolt-in" swap from a Chevy or were small blocks an option?
- The vehicles condition; looks like original paint, bed wood has rot, but you can stand up in it. Dings and dents. The drivers door is bent in the front edge because the little restraining bar broke at the pin. The door was opened too wide as a result, and the front fender edge did the creasing. Is this a common fault?
- The dashboard instrument cluster has three round holes for gauges, but the far left one is just a gaping hole..what went there?
- The truck has 8 lug split rims. Are there any common later solid rims that will accept the original GMC hubcaps?
- The blue paint is worn off and there is plenty of surface rust, but the fender corners are solid ( I'm in Southern Califonia). There is a little stress cracking in the rear upper corners of the bed. I don't know the mechanical condition yet, it's sat for years. I plan on making it a clean work/tow vehicle.
Is there anything else I need to look for?
Thanks for any help!
P.S. I've always thought the GMC "dog bone" grille looked great!