d46 rears with 3.36 ratio

Trust me, 550 hp should be adequate.
You said you worry about damage with the 3:36's, jacking it to 700 hp could create problems you don't want or need, reduced engine and driveline longevity, breakage, a drop in fuel economy, higher EGT's, higher internal heat and stresses inside engine, as well as transmission and diffs on long hard pulls, accelerated tire wear, frame stress to.

It's all relevant, one weak link in the chain is one too many.
The truck my friend drives was built from the frame up with a plan before they started, not a trial and error situation where they put a big engine in a truck and replaced components as they broke, which is often times the case.

That's what I did when I was a young OO, put a bigger engine in the truck with a tune on it, within Cummins spec for high altitude, ran pretty hot at sea level, pulled real hard, and inside of a couple months I replaced and upgraded the trans, the clutch and broke the power divider at which point I said screw it and put a complete rear suspension and housings with new brakes and rebuilt diffs.
About a year later the new engine blew up, which was Cummins fault, big piece of junk.

 

Don't feel stupid, you caught yourself before you went and did it.
A 550 hp Cat is already a beast of an engine and a truck is not a race car.
Keep it in proper tune, keep your filters clean and you should have all the power you ever need.

If you happen to have an EPA 7 ACERT engine you might ask the Cat gurus about upgrading to a higher hp using Cat's parameters for tuning, but use a low torque version if your tranny is only rated for 1850 ft/lbs.
Can't tell you what's involved, thinking it's a little more than reprogramming.

I kinda like that long flat curve for 625 hp low torque engine, 1900 ft/lbs is still a lot.
http://hollonoil.com/PDF/CATC15KINGOFTHEHILL.pdf

 

Like the torque curve on the old maxidyne lol