cab is coming off. Could use a little advice on engine work
 

OK, So I bought a nice rust free cab from a 6.0 truck, and am getting ready to start the swap project. I realize that I'm going to have to swap out all of the wiring harnesses, and there are some other subtle differences, such as where the PCM mounts. Pretty sure I have most of that part worked out.
The advice I could use is, what to do the the engine while the cab is off. I have recently dome manifolds, up pipes, turbo, exhaust, 180cc injectors, and a new Hydra. I'm still getting codes on Cyls 4 and 8 on the contribution test. I'm hoping that when I pull it back apart, it's just bad cups, since all of the wiring checks out as of now. I plan to replace the oil pan, oil cooler, plenums, and anything else I can find leaking. While it's all apart and the engine is getting pulled to do the oil pan, should I just have the heads gone through? Or replace the heads? I have recently come across some articles about the heads rusting through. Then at that poing, where do I stop? Or do I stop? I don't want to get into another 6 or 7k into this project, but, if I'm doing all of this, I'd like to get another 10-15 years out of it. I'm just shy of 500K on it now.
Thoughts? Comments? Criticisms? Thanks for any input

Replace the oil galley plugs on the back of each head.

I did that as well, because I had (have) a pretty decent oil leak going all over my starter. Passenger side not a lot of fun. And it still wasn't my leak. LOL

:-hair
Wouldn't it be easier to buy a rust free truck from the sunbelt and rebuild that?

Never been known to do things the easy way. Already have a rust free bed. Cab came with full interior, trans is in good shape. Recently switched to 410 axles, new brakes all around, new hub assemblies, Runs pretty good with the exception of the 2 cylinders with low contribution. At this point, it's more about the truck I drove off of the lot in 2001. Obviously parts will be different, but to me, its still the same truck

of you’re gonna be married to it 6-7k beats 80k to get a new one. Biggest issue is if it gets totaled or stolen. Make sure you get a insurance policy with stated agreed upon value not market value