Justin,
Based on my experience with the ZMJ engine (and once you've seen a K-jetronic you've
seen them all), the plunger goes thin side down. Resist the temptation to take the
distributor apart. It'll surely leak afterwards, and Bosch will sell you only complete
distributors at a fearsome price (I learned the hard way). If the distributor leaks gas
along the plunger your up for a replacement, as there a no rubbers to replace. The
plunger prevents the distributor from leaking just by fitting tightly into it's
housing.
BTW: you're talking a least 5 BAR (don't know PSI's) pressure in the high pressure
circuit, so watch your rubber hosing.
Paul