As long as it's just oil with no crud in it, you are fine.
Speaking of which... IDIs are /filthy/ motors. Huge ring gaps, tons of blowby... that's just how they are designed.
What this means is: Frequent oil changes. Don't skimp on them. The manual says 5K normal service, 2.5K severe... I go 2.5k.
Any 15W40 oil should be fine; I use Mobil Delvac because it can be found with large mail in rebates.
Oil filters - Use one for a 7.3 PSD. FL1995 or equivalent. They are 1 quart longer(11 quarts total oil capacity).