Bonus post! (Long post...)
Figure I'd keep this one separate from my last post since it's a pretty significant aspect of the project. Enough to warrant its own discussion.
So, I bought a coilover. Just one, though.
Going with a Fox 2.0 emulsion coilover. 10" travel (9.25" actual), 7/8" shaft. Fox seemed to be the best overall option...cost, parts availability, service availability (local). The thing I've learned is that each additional "feature" or upgrade on a coilover adds $50-$150 per shock. My "budget" Fox option was just under $300/ea, while the piggy back reservoir ones I wanted ran almost $500/ea.
I'm seeing about 7" of vertical travel; 3" up and 4" down. Squeezing more up-travel would require lifting the truck more, and beyond the usefulness of using radius arms. Ride height should amount to about 7"-8" of lift from stock, which is still another 2"-3" above what I was running with the SFD. Numbers-wise, things are pretty much on target for my needs.
Springs are the next thing I need to order (well, and another coilover...they only had one in stock at the site I went through at the time). I'll have a dual rate setup, which uses two springs, though it'll be unconventional setup I suppose. Rule of thumb is:
The lower spring should be equal or longer in length than the upper spring.
The lower spring should be equal or higher in spring rate than the upper spring.
In a dual rate setup, there's a primary rate produced by both springs being in series, and then a secondary rate...which is just the rate of the lower spring because at some point, the upper spring will stop compressing. Problem with the conventional approach is that the secondary rate is always, at minimum, double the primary rate.
For example, Calmini offered a 300 lb/in + 300 lb/in 10" coilover setup for their Xterra SAS kit. (This is about as best of a starting point as any considering the 1st Gen Xterra has almost the same curb weight as the R50 and loses and gains pretty much the exact same parts). A 300/300 spring set produces a 150 lb/in primary (it's not an average) and 300 lb/in secondary rate. But, that's what I don't like...the primary rate seems perfect, but then there's a 150 lb/in rate spike. Just seems like too much.
I set some target rates around the stock numbers (150 lbs/in), OME numbers (200 lbs/in), and also on a few dual rate springs OME offered for similar vehicles. OME's dual rate gaps are closer to 40-120, which I'd like to think led to a far more comfortable ride setup (I do trust OME in this department).
The only way to lower the gap is to put the heavier spring up top. So, that's probably what I'm going to do. Currently planning on a 9" 350 lb/in upper and 12" 250 lb/in lower. That'll give me a 146/250 setup. Notably, the OME MD setup for an FJ80 is 170/260, and 150/260 for a Pajero/Montero, which are fairly similar vehicles (FJ being a bit heavier).
There's some other math involved, but I should be within the range I need to be. Unfortunately, if this approach flops, I'll learn a pretty valuable lesson about coilover springs. They're not cheap, but Summit has some options that'll shave a few bucks off.