I picked up an '87 several months ago and have been cleaning it up and learning as much about it as possible.
I'm pretty sure that the pick of the litter is the '88 because it is the only year with a PWK Kehin carburetor. All others have a Mikuni round slide.
The forks and front brake and wheel are the same as the early E-series bikes ('89-92), but the triples are different. The front brake is a single pistion affair, which is better than a drum, but certainly not as good as a more modern brake. The rear brake is a drum, but I haven't actually ridden the bike more than around my yard, so I can't testify as to how it performs on the trail, particularly in wet conditions.
The rear suspension is an early Uni Trak design that uses a push rod from the swing arm to a rocker arm under the seat which actuates the shock. The rocker arm uses pretty generic needle bearings, which are probably easy to replace through a bearing house, but the push rod has heim joint/spherical bearings that you just can't find from All Balls. There are no linkage bearing replacement kits available from any vendor, so you'll have to forage to find what you need. I managed to get an OEM spherical bearing from Babbitt's, but it cost $76, and the bolt it rides on and the special seal is unavailable. It probably wouldn't have been too tough to fab up a correct bolt, but the seals area a different matter, so I wound up buying a good condition one from someone parting an '86. But the great thing about this archaic set up is that each pivot, including the main swing arm pivot, has a grease fitting, so you might potentially keep the bearings in good shape longer with minimal work.
The '86-'88 bikes have a trick electronic trip meter and clock that is resettable up and down by hundredths, which is exactly what you need for old-school time keeping enduros. They seem to be much more reliable than the mechanical odometers that the E and H bikes came with, but replacing the electronic pickup at the hub or, heaven forbid the whole unit, is pretty expensive.
They have a 6 volt electrical system, so don't expect to find replacement light bulbs at Auto Zone.
Regarding the motor, it shares a lot of bottom end parts with the E and H motors, but the shift shaft isn't one of those parts. Mine was stripped and badly welded, and I had to find a good used one on eBay. The top end has a plated cylinder with an early version of KIPS using two small rotary sub valves but no main valve. They seem to be more robust than the problematic E sub valves, or at least that's my impression because the KIPS in my '87 were perfect and they looked original. The sub valves in both my used E-series motors were trashed when I bought them. The stator and flywheel are not the same as E and H bikes, but I believe Jeff Fredette has a method of either repairing the stock stators or retrofitting them to work with newer stators. Pistons, small end bearings, main bearings, tranny bearings, gaskets and seals are all easy to find on eBay.
Ergos are typical old-school--big cushy seat, narrow bars that feel low and close, skinny foot pegs, pretty low seat height. The bike feels very thin despite the large tank because of no radiators and a pipe that tucks in neatly. It also feels quite light wheeling it around the garage, but I haven't weighed it yet to see if that's just an illusion. It has a great hand hold under the rear fender that is reinforced by the subframe, which makes it easy to lift onto a stand or out of ruts.
It has a weird air filter. I had some trouble getting it from No Toil (one of their premium reusable filters), but I eventually got the right one. The airbox is very waterproof, with an intake just at the lower margin of the seat.
I haven't put any real miles on mine yet, but from what I can tell around the yard is that it has very nice low-end power and will lift the front end easily in the lower gears. Once I get a few shake down trail rides on it, I very well may take it to a hare scramble or enduro this year just for fun. I don't think I'll be dicing it up with usual competitors, but it should be a fun, comfortable bike to cruise on.
A worn rear drum can be a drawback though, if they are worn badly even new shoes won't fix as the shoe actuating cam can just go so far. You probably could get the hub machined to take a sleeve pressed into it if you had to. The engines were bulletproof, never had a problem with mechanicals. I did have a coil fail once. The 86's had bad rims that cracked easily (same as the 250's) and I had a shifter spring break (also same problem with the 86 250 I had). 