I've found 4.56s and 35s with the TBI350 to be a decent combo. Still very power limited but at that point it's mostly a power problem, not a gearing problem. I will say you should not be afraid of "over gearing" it. Your 30% overdrive will soak up a lot of gearing. If you're serious about 37-38" tires, at least 4.88s and maybe even 5.13s are the way. I'd do 5.13s. We've geared a couple GMT800 trucks with 6.0L/4L80 combos on 37s and 4.88 puts them at about stock rpm for a 2500 truck but you have a deeper overdrive and less power. Thus the 5.13 recommendation.
I hate to be the guy recommending smaller tires but with limited power, I'd consider keeping the tires smaller and like was mentioned earlier, maybe bail on the 14B front too. A GM D60 is a really solid system that seems to have gotten a bad rap somehow lately but they have always been able to take about anything you can dish out in a K5 on anything less than a 42. Keep in mind also that once you go past about a 37, your 241 quits being a rockstar and becomes something you need to think about.
Really hard use is not a slippery slope, it's a cliff edge you step over. Past 37s and you need strong axles, hydro assist, the tires themselves which are typically on beadlocks, power to move all of this with a trans that can take it, T-case strength and so on.
Moral of my story, put 5.13s in a GM D60 front and your 14FF rear, run 37s and go camping. Coilovers in front with our leaves in the back is a great system that will drive nice and have really good offroad capability too. And our coilover system works really well with a GM D60.
