I would ASSume the engine is good, until unless its showing signs its not. Your assessment of blowby, good compression (equal on all 4 cylinders also), running smooth, starting easily and quickly, etc. would lead me to believe the engine is good to go for another 500,000 miles, at least.
My 1984, bought new (first new vehicle I ever bought! got 450,000 on it before I got hit, then did another 154,000 before I traded it in on a 4wd V6 MMax in 1990!. Still ran perfectly. I ran 18 lbs boost with some added fueling, and a ported turbo, as well as match ported head, intake, and gaskets. I used it as my DD construction truck, hauling and towing 3 to 4 times weekly. Then every other wkend, hooked my 4000lbs Stamas 22 ft Cuddy Cabin fishing boat and galvanized tandem axle trailer to it, punched it in 4th gear, and proceeded to smoke it at 12mpg all the way to Gulf SHores, AL (200 miles approx) at 55-0 mph. up hills slowed, downhill sped up. I did use 4th gear as it was direct drive and stronger for towing. ALso, better torque at the slower speeds towing. At 80, unloaded, it was better in 5th, of course.

I NEVER did ANYTHING except maintain it (religously, oil changes with Castrol every 5000 miles, and Amsoil in tranny and diff every 80-100,000 miles. (Didn;t know I should have sed Rotella etc, and had to flush engine at 200,000 miles from oil solidifying 9Gas Castrol 10w 30). Also burned up turbo's at 120,000 miles approx, so 4 before I chnged to Amsoil, and ended ALL issues re oil in the little engine. Extended the changes to (10,000 miles with analysis)after the flushing of the goo from Castrol in the Diesel and torched turbos.

The trans bearings gave some problems twice, they had to be replaced, in 4th and 5th gears. Seemed it was common, as my GF had a 1985 black 4wd diesel 5 speed as well which had the bearings replaced as well.
These were truly GREAT vehicles, and if maintained, seemed they'ed last indefinitely! I USED mine HARD, towing all kinds of trailers, and the cruiser to the beach on wkends (we'd camp on it anf fish all wkend) then tow it back for 3 yrs until I could afford a lot and trailer and kept it there.