Depends on what the plans for the axles are. If this is for a rock-crawling buggy that's going to be pushing BIG tires (as in 38"+), it might be a toss-up between 80 series axles and domestic big boys like D60's. The front 8" differential would be considered the weak link of the 80 Series axles, and that's really only if you're moving really big tires or massive amounts of torque.
Anything 37" tires and below, you'd be hard-pressed to find a better upgrade in the US-spec Toyota market.
Be advised that Toyota parts in general are fairly expensive (gear sets, for example), but since you're a Rover dude, you're probably as used to it as we are.
One more thing. I don't think you can run 15" rims with 80 Series axles unless you go with a goofy offset, so plan on having to run 16"+ rims. Don't know if this matters, but you probably wanted to know.
Oh, and US-spec 80 Series front axles will have drive plates instead of manual hubs because the trucks come full-time 4WD from the factory. I presume you can upgrade these with Hilux (Toyota mini-truck) hubs, but you'll have to ask those smarter than me.