Ring startech in auck, genuine/oem plug leads for a M104 for around $150, check the coils too, there was a supersession to a newer type due to misfiring, older ones can be modified by running a couple of beads of mig down the outside to prevent tracking.
M104 vs Jeep six is like comparing a DC3 with Concorde.. The old pushrod six is a good motor, also way too tall to fit in a Mercedes engine bay, the M104 is in a different league technology wise/ 1/10th the weight..
And a million times better than a RB motor.
Drop in a 3.2 M104 and upgrade software and watch it fly.