You can't lose. You've received good input already, but since this is similar to "voting", here's mine:
If you like being first off the line at the light, you need to get the auto. Otherwise...
ETH (HO), 6 speed, 3. 54, BD Brake and 4" exhaust, EGT, boost, and fuel pressue gauges.
ETH (HO) - Power gain over ETC is marginal, but you get stronger factory clutch, that much easier to BOMB with SBC when you wear out your first one.
6 speed - A gear for every speed. When you get on a big hill, dropping to 5th gives you good speed and "direct drive" in the transmission, which is your minimum wear configuration for heavy loads. Also, having manual makes adding an exhaust brake easier because you don't need to spend more money on auto upgrades.
3. 545 - RPM in sweet spot at 70 mph, mpg spot at 60 to 65 mph, and you're not towing "heavy". The 3. 54 vs 4. 10 decision is really too close to call - strong supporters on each side of the fence, but I agree with previous posts on 3. 54 w/manual, 4. 10 w/auto.
BD Brake - 'CAUSE IT'S FUN! Oops, I mean because since I got one, with the shifter mounted switch, I don't even get that red dust on my front wheels any more. That's a major drop in brake wear; BD is one of few options that will eventually pay for itself. Side benefits include speedy warm-ups, ability to leave it idling without fouling it up, and a handy mounting place for a post-turbo EGT probe (pre-turbo better if you BOMB heavily, post better for turbo cooldown monitoring - and know that some strongly disagree and believe pre-turbo is the only way). My main point is that BD port makes post-turbo mount EASY; if you want pre-turbo instead that's fine and has benefits.
4" exhaust - HO generally considered to have "marginally high" EGT's out of the box; with 4" exhaust my peak EGT's have dropped 150 degrees or more. You're towing - get it.
Gauges - Protect your investment - don't get stranded. Details MORE than adequately covered in numerous other threads.
Good luck, and Enjoy!