[BR3W CITY]

just as a reference #, around 3 or 4 down (so -3 or -4) from the deck is what GM uses. Most of the time 0-4 down will function, and some guys have run more extreme than that and not had a catastrophic failure, so long as they can end up at the rear end with a driveline angle that doesn't bind. Extreme angles can cause issues with ujoint breakage.

You can read tons of articles on how the driveshaft and rear axle interact in terms of complimentary, matching, or negating angles. Its a topic of its own.

The main reason that you see the "0-4" on LS engines is generally related to the steam system. The slight downward angle encourages the air to follow the high point in the heads to the steam crossovers and then vent. Its one of those things that has 50 pages of stuff on it at LS1tech, with opinions all over. Its usually not too hard to get somewhere in the o-4 range.