I dunno about what ya wanna do. The best thing you can do IS READ OTHER BUILD THREADS. This will tell ya what people like and what they don't.
4.7:1 gears would be a great upgrade. I'd recommend that for one of your first mods. 5.29:1s is the second mod I'd recommend. Then lockers. That's me, though. Whatever you want is worthwhile.
Also, upgrading to a w-56 would be a good thing. It's a five speed, and it's much stronger than any L or G series (me thinks). Plus, it's a ton cheaper than a HD unit ($150 or so versus Marlin's $1000)
I did notice your 456:1 is not correct. I guess you multiplied your tires size in that? I dunno. Tire size has nothing to do with crawl ratio. That comes in later in how fast you actually go.
Keep your questions coming!!!
