The parabolics are a plus, either way. If you drive it on the road, the ride is much smoother, more consistent, and more bearable on long hauls. Slightly taller ride height means that better selection of rubber will be available. Most series owners go with 235/85/16 for rolling stock. Parabolics allow thwem to fit without trimming.
Off-road; parabolics offer more articulation, less jounce, and a softer ride over the rough stuff. Once again the ride height helps as well.
Either way; if you end up having to replace your springs; the paras are not much more expensive than stock units. You can get a complete set of all four, with new hardware, new u-bolts, and greasable shackle fittings with zerks for around 800 from Great Basin Rovers.
16" wheels were stock on Landy's. Very rarely will you find 15 inchers on a SIIa or SIII. The warns free wheeling hubs were aftermarket. Sometimes put on as a dealer option, but most dealer add-ons were made by Fairey, the same company that made the overdrive unit for them, and some older winches. Warns are only seen put on by dealers statesside. I have the warns on a set of 64' axles I have laying around.
If you do a full restoration; plan on keeping it forever and having it go to the kids and grandkids. For you will never get your money out of it, if you do it right. If you make a trail rig / daily driver / weekend toy; you might break even on it. The trucks asking high money on craigslist and ebay stay listed for months and months, and usually have the reserve dropped half a dozen times before selling.