If you're doing a gear swap, and keeping the 10 bolts, you'd have to also change carriers to go 4.56's also since the cut off IIRC, is 4.10 and down, and 4.56 and up. errrr orrr am I thinking of 14b Full Float? At any rate, consider the cut off and the need to swap for carriers too as those are added expenses, and for 1/2 turn I personally don't think it's worth that added expense when you're talking just over 4 turns, or just over 4.5 turns for 1 wheel revolution.
However, if you don't need the carrier swap and buying gears for a gear swap, even with 33's, I would not be afraid of 4.56's at all. If you're running the OD trans, even being a 700r4, with 33in tires I wouldn't be afraid to use OD with 4.56's and towing. Sure wouldn't do it with 3.42's, 3.08's or 2.73's. If what I was towing wasn't all that heavy, I'd also use OD with even 3.73's or 4.10's. That's the whole point of using lower gears, is to take the strain off the powertrain and engine including the transmission.
Now that I go back and read that you have a 3.73 LSD rear axle in the truck now, I'd leave it alone and just get the front geared to match. 3.73 with 33in tire and staying in D wo using OD to tow really is not all that bad at all. Keeping those rpms up is actually good. Small blocks love rpm. You get the rpms to low, you'll lose power and may end up going slower and putting more strain on the trans and motor. Honestly, I think I'd leave the 3.73's and tow in D. 700r4 has a lower 1st gear than Th350 and Th400, so even with 3.73's, it should take off pretty good with the 3.06 first gear that the 700r4 has vs 2.52 and 2.48 first gear the Th350/400 has.
JMO, I'd either keep it 3.73's and tow in D, or go 4.56's use OD to tow too, just not pushing it hard and keeping an eye on my trans temp. That's just me though. There is also such things as a Super Hold Billet Servo for 4th/OD gear in the 700r4. If and when I get to build a 700r4, I full intend to tow in OD but I'll be building it with things like that Super Hold Billet Servo, wider 2/4 band etc for that reason.
The reason it's suggested to NOT tow in OD is so you're not slipping that 4th gear clutch pack and band which creates wear and excessive heat. If you've built the transmission with higher and tighter clamping force on the clutch packs, a wider band with more clamp force, then you shouldn't have slippage that creates the heat.
This is why I've always said I want to build a 700r4 and be rough on it, find the weak spots and build it again and again until I've resolved all those issues and finally have one that will hold up.
