Need a little horsepressure.

You need to post engine serial number. CPL # on the engine and fuel pump. Anything you know that has been changed.
Always check your throttle lever breaks over, fuel pressure under load and the AFC before making changes. It is hard to get more out of a sick sled dog. Just my opinion.
Then someone may be able to give you some good direction.

 

That looks like a new tag that was never stamped? Look for a tag on top of the fuel pump. The reason I asked for both is that if they match you have a good chance that's what you have. Now you may want an injector number.
Point being you have no idea what engine you have. We would assume something with high output in a Pete. With a tag like that I would assume it is not factory. It could be a 315. The compression ratio and timing would never allow you to tweek it to 500 HP.

 

Oh: And it is blue?
Someone posted some pictures of a Cummins they painted red white and blue. That was cool, different, to each their own.
Cummings did paint some blue. The one I know of is a small cam made in 1971. Can we get a pic of the cam follower boxes on the left side of the engine?

 

You will NEVER get 500 HP out of anything 87' NEVER.

If you by some miracle did that block is going to grenade on you, overheat (Wait until you discover how small some cummins cooling really is...) or grind themselves to dust inside or simply burn themselves out.

And for just that little bitty flat part of cali? Impatient are we?

Title that to me, I would love to have a older iron to nurse along around here doing this or that several times a year. Not in any particular rush.

 

If the engine is original, post the last 6 of the truck and i should be able to get the engine serial number

 

.