35's are pushing it for a stock d30, but the D44A could handle it if you're not crawling. And with some C-gussets and chromolly's in the front, you'd probably be fine for mud and sand. I wouldn't swap axles unless you're gonna crawl it, though. That's just my opinion. I have a close friend that wheels the crap out of his JK Sahara on sand and mud with a stock D30 in the front and he's never broken anything. He only upgraded when he decided to start hitting rocks with us.
As for my build, I'm having a hell of a time getting a hold of the guy that has the other set of axles I found. They're the same thing, HP44/60 but out of a '79 F-250. They're identical to the first set I found, though. Hoping he gets back to me this week so I can go ahead and buy them and start tearing them down. It'll take me a month or 2 to get all the parts I need to build them, but I want to get started as soon as possible. The lower spring perch on the passenger front side is literally falling apart, so I want to get a new set to put under there ASAP so I don't have to spend any money buying/welding a new spring perch on this stock axle.
2003 WJ Overland 4.7 HO, Clayton Long Arms, Teraflex 4.5" coils, JKS adj trackbar, JKS Quicker Discos, 17x9 Eagle Alloy Series 185, 285/70/17 BFG KM2, cut fenders/bumpers