This is sure a puzzler!
You've done some good diagnosis; the problem is obviously not fuel or
glow plug related.
It's time to check the valve and injection timing, also the valves' gap.
Remove the valve cover. Turn the engine (a wrench on the nut of the
power steering pulley should do it) in the correct direction until the
notch in the thrust collar immediately behind the cam's chain sprocket
is aligned with the groove cut into the left side of the front most cam
support tower. That's TDC for #1 on the cam, now read the crankshaft
angle off the harmonic balancer - it should be between 0 and 5 degrees,
especially if the engine has be run only 78 K miles.
If the angle is significantly different from (0 to 5 degrees) then the
chain has jumped and the cam needs to be reset to be correct with the
crank. That's a possibility but not probable.
The next is to check some of the valves' gap. .004 INCH for the INtakes
and .015 INCH for each EXhaust. Check each valve with its cam lobe
pointing 180 degrees away from its rocker. WRITE DOWN each that you
check to avoid duplicating your work. Adjust the CAP nut and lock the
adjustment with the lower nut. 14 MM straight wrenches can be used if
If the cam is correct and the valve adjustment reasonably OK then the
injection timing is suspect - probably badly retarded, beyond adjustment
range. That means someone removed the injection pump and installed it,
probably 24 degrees retarded. Again, #1 cylinder is the reference point.
There are various methods of checking the fuel delivery - drip tube,
water bubbles etc.
Or you can turn the engine to 24 degrees BTDC (be sure its for #1 - that
both cam lobes are away from its rockers) and remove the injection pump.
Its drive gear has an intentionally mission tooth - that should be
aligned with a groove cut into the collar immediately behind the gear.
Reinstall the pump and check the fuel delivery. Turning the top of the
IP toward the engine will advance the injection timing, turning the top
of the IP away from the engine will retard the timing. The timing isn't
too critical if its basically OK, you can adjust it later - easy
starting but poor power indicated retarded injection, preignition too
far advanced timing.
You have your work cut out. Hope this helps you.