Two or three different problems, I think.

Smoke: I'd start with injectors, get a set from Greazzer (forum member), or buy Bosch rebuilts and send them to him for test/adjust of pressures.

Oil: Welcome to the club! You'll need to clean off the entire engine, and then carefully observe where the oil is leaking from. Could be as simple as the o-ring under the injection pump shut off lever or as complex as the oil pan gasket. May be multiple places, just need to dig in and figure it out or pay a mechanic to diagnose and then decide if you want to do the work or pay them.

Noise: I agree with a leak in the intake or exhaust, nothing to do with vacuum. You can confirm by plugging the vacuum lines to everything except the brakes, and then going for a drive. Transmission will shift REALLY firmly, but a short test drive won't do any long term damage.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC