I'll take a stab at it for ya:
1) correct, woodgrain is Cheyenne or Cheyenne Super trim level. If you have woodgrain, it's likely been added during a refresh.
2) what Leon said
3) see pic below, this is your original seat cover, RPO 607 - houndstooth would be a different code/description and couldn't be had on anything except a YE9 Super (as Tim mentioned).
Always lots of confusion on the cloth seats - Custom Deluxe (bench) is "Cloth Trim" (below, Custom Deluxe only) and Cheyenne Super (bench) is "Custom Cloth Trim" (Cheyenne Super only - aka
Houndstooth).
4) Grill and surround is identical on all 72's regardless of trim level. Chrome bumper not part of the Custom Deluxe pkg - if not on SPID, it's a PO add-on.
Also note your windshield has the bright trim, also not part of the Custom Deluxe pkg.
(do your cab and SPID VINs match?)
5) Best option for how you posed the question (without losing originality and for what the truck was built for) is GV O/D. Reversible upgrade, not that you'll ever want to - but you retain stock HD trans, stock rear, and GV O/D unit is bulletproof, won't be the weak link. 200R4 will not support intended original use of a C30, not strong enough. Nor is a 700R4. 4L80E is really the only automatic option I'd consider IF you wanted to change over to auto (since a TH400 has the same output ratio as your current trans), but I'd stick with the stock, well, stick
and add a GV O/D unit.
Look fwd to the SPID - beautiful truck, congrats.