slant 6 oil weight

I would look for a dual-rated oil (eg, API CK-4/SN) with a Ford WSS-M2C171-F1 rating (1000-1200 ppm phosphorus) and the only one I'm aware of now is Petro-Canada Duron SHP 10W-30.

All-Fleet Plus 10W-30 Valvoline
Napa Value 10W-30
Rotella T4 Triple Protection 10W-30
Rotella® T5 Synthetic Blend SAE 10W-30

hundreds meet that spec here...
https://parts.ford.com/content/dam/...iesel_Motor_Oils_Meeting_Ford_WSSM2c171F1.pdf