Interesting project. If your goal is to have the truck "driftable" in the sense that the vehicle is not unduly disadvantaged for the occasional drift duty, then you will surely want a bit more steering angle than what you have achieved even now. There's no magic number, but from my experience, cars with <40 degrees of angle are generally difficult to "balance" while drifting and will leave drivers frustrated. The corvette is a great example of an exceptionally well handling car that is borderline hopeless on the drift track on account of insufficient steering angle. Unfortunately, to escape this you may be facing further compromises in your front suspension design which you may not feel comfortable with.
Barring a complete redesign of the front suspension system for drifting, the next best thing might be to just go the easy route and simply run less wheel back-spacing, and a narrower wheel if fender fitment is an issue. A big compromise this might appear, but a compromise that could be made exclusively for drifting and reverted for any other activity the truck sees duty. To keep the steering in check with the wider wheels installed, you could whip up some adjustable steering stops or removable steering rack travel limiters to keep the 275s from hitting the frame rails at lock.
With the narrower wheels and lower backspacing, you may have concerns with the lowered grip level and increased scrub-radius. While these might not be optimal, the tradeoff for the extra steering angle is very much worth the sacrifice, and the vehicle will perform much better and be more rewarding to drift.
Also, as Mike said, check that the brake caliper won't be hitting the shock or lower control arm at full lock.