While certainly not necessary, I still maintain it is a good idea. The 103 has the small pump and the slow spinning gear. The 104 has more oil demand and has the larger pump. The 603 has even more demand and has the larger volume pump and has the smaller (faster) oil pump gear. (the 603 also has a higher pressure relief valve spring) All of these engines have almost identical reciprocating assemblies, the differences are the consumers in the oil supply. There is a correlation between the oil demands of the engine and the oil pump output. Given that he will be looking right at the oil pump gear and chain while swapping out the rail, it would be an easy swap to switch out the oil pump drive gear and chain for more oil volume at lower engine speeds.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff