A better engine swap would be a turbo OM606, with intercooler. Keep you existing injection pump. This swap has been done more than a few times before, and the resulting car has more power than the original. Going backward to an older 603 will give you less power.

I'm still convinced you've got a sticky lifter, just need to switch to Mobil 1 oil and driver her for awhile.

__________________
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