[sags]

I asked the same question when I bought mine a couple years ago - a 1965 with a 250 (which turned out to be a 230), 4 spd on the floor. To date (and in order) here is what I have done:

I cleaned and adjusted the brakes as the very first thing. Mechanics actually tried to convince me to keep them.

1. Wife sprung for having the seat redone. Added seatbelts.
2. Disc Brake swap front including power brake booster and dual mc, TR ends- kept the 6 lug. Seriously, I called Langdon's asking about headers and carbs the first week I bought. And although I am squarely in middle age, Tom answered the phone and said to me, "young man, the very first thing you must do is upgrade to disc brakes." When Tom speaks, many of us listen!
3. Found out from the brake swap where I added 2" drop spindles that the previous owner had cut a little more than I thought so I went back in with proper drop springs (2") and shocks. Raised the front up an inch and a half and keeps it from bottoming out. Also did 4" drop springs and shock relocation on the rear
4. Added front and rear sway bars. This makes a huge difference as the truck stays under you around corners. Was going back and forth about power steering but like the old school except after days at the gym.
5. In the effort to resist V8 fever from the costs associated with having my engine rebuilt, found a 230 on craigslist that was rebuilt with the paper work, repainted with the exact same tranny. Just as my engine had an HEI, so did the new one and also had a Petronix ignition. Swapped these and sold the old motor and trans.
6. New radiator.
7. I have Clifford headers in a box in the garage and will be getting clifford intake and carb soon. That should hold me for a while - approaching three years now.

Have fun with whatever you choose. Mine is not a daily driver and I have toyed with the idea of T5 if only to get rid of the granny gear.