2001 Chevrolet Tahoe LT, 4x4, 5.3L engine. Modifications: cold-air intake, Doug Thorley Headers (no EGR tube)
Mileage: ~176k miles
Location: Atlanta, GA
Experience: Novice

Summary: I installed Doug Thorley headers when I put in my new catalytic converters (O2 sensors and cats were toast) about 5 months ago, discovered a broken exhaust manifold bolt on the rear driver's side (the worst place possible). Had two different mechanics attempt to drill out the broken bolt, during which they damaged the mating surface on the cylinder head. I have also thrown away my stock exhaust manifolds (which were the original manifolds). I have since moved to Georgia and figured out that their emissions test include a code test for the EGR functionality, which I no longer have. I cannot get my car titled/registered in GA until I pass an emissions test, and I have a massive exhaust leak than cannot be fixed with fatter gaskets or otherwise (I have already tried) . Outside of the exhaust leak the car runs 100% fine, but the exhaust is leaking into the passenger cabin and is highly toxic/damaging to the lungs, so it is effectively undriveable. The interior/exterior of this car are also pretty much flawless so I don't want to just scrap it either.

Issue: It looks like I now have to 1) replace the driver's side cylinder head in order to get a proper mating surface for the manifold/header and 2) go back to the stock-style exhaust manifolds. HOWEVER, both the cylinder heads and the stock manifolds are no longer in production through GM original equipment manufacturers/suppliers and the Dorman products are complete trash. I don't want to have to repair these parts every 2 years, especially not the cylinder head, which is notoriously difficult to maintain a seal on the head gasket once the original has been replaced. There are also many parts that say they are "compatible" between silverados, tahoes, yukons, etc. and yet they are slightly larger or smaller, which makes an enormous difference for this particular repair in terms of bolt hole alignment, seal, etc.

Solutions: I am either looking at 1) hopefully finding a cylinder head from a dealership for the driver's side (cost is not the issue, needs to be reliable) and picking exhaust manifolds off of a junkyard car (and having them machined) or using aftermarket, or 2) replacing the engine altogether with a crate engine and using "picked" manifolds or after market manifolds (hopefully there is another option than Dorman).

Questions: 1) is there anything else I can do to fix the mating surface on the cylinder head without removing it, in order to fix the massive exhaust leak that now exists, 2) are there any parts manufacturers that make a decent cylinder head with gasket kit and/or exhaust manifolds (with EGR port), 3) if I am already going to replace the driver's side cylinder head, should I/do I need to replace the rocker arms as well?

Many thanks for your help.

Gray