I have been tossing and turning, surfing every post I can find that seemed related for 2 weeks trying to get answers. I am on the verge of rebuilding my 1998.5 as soon as I buy a newer rig to daily from now on and have this one as a toy. I’ve read more than one post about 6.7 crank in a 12v. And ppump on a 6.7. I was looking at stock bore or maybe 20 over(is anything bigger safe?) with a 6.7l crank and it seems I need shaved pistons to make stock compression. Are the crank gears interchangeable? When I rebuild it I’m going to try my hardest to get the crank polished and balanced, pistons coated, rods polished and hardened. And maybe my head milled off if the budget will allow. Any insight is appreciated!

I do believe they are fully interchangeable. But I think that just raises your displacement to something like 6.2 or 6.4l I can't remember. 

2 hours ago, pepsi71ocean said:

I do believe they are fully interchangeable. But I think that just raises your displacement to something like 6.2 or 6.4l I can't remember. 

If I bore it .20 over and use a 6.7 crank it will make it a 6.151L but compression will be like 21:1. So ide have to have the piston shaved or custom piston.

They definitely are interchangeable...I've heard of a few 5.9 cranks being used in 6.7 blocks with special length rods that keeps the same compression ratio as the 5.9 with a bigger displacement (6.2-6.4).  The 6.7 block is engineered a little differently than the 5.9 to be stronger.  But I have not heard of any the way you mentioned.  21:1 down to 17.5:1 seems like a lot to overcome.  I think the 6.7's 18.1:1 compression ratio is also too high.  They have certainly been more prone to head gasket failures than the 5.9s at 17.3-17.5:1.

On 10/21/2019 at 6:32 AM, Waydin_Stewart said:

If I bore it .20 over and use a 6.7 crank it will make it a 6.151L but compression will be like 21:1. So ide have to have the piston shaved or custom piston.

Why not use shorter rods?