Header Complications

I've spent at least 4 hours scraping old gasket off the headers and the components which attach to them. Most of that time (>90%) has been focused on the exhaust system. Unfortunately, I have learned from this experience that sharpened scrapers, sand paper, and chemical gasket remover are not sufficient to remove residual exhaust gaskets from headers. I'm going to have to apply different methods of removal to ensure I don't reassemble my engine only to find I have an exhaust leak. I've included a picture of each header below show my current progress.

This is the passenger side into which I've put most of the work. Despite my efforts several areas of residual gasket remain (red arrows). Although it may not be apparent in the photograph, rubbing a finger over those areas makes the imperfections very apparent. I'm most concerned with the lowest arrow in the picture as the area covered by the gasket is so much smaller.

The driver side, which I has not had as much scraping or been cleaned yet, looks worse but does not have as many imperfections.

Possible solutions:
1. Use a large flat sharpening stone to remove the excess material and flatten the surface completely.
2. Use a handheld grinder/polisher, such as a Dremel tool or angle grinder, to remove the excess material and polish the header.
3. Find a exhaust sealant to use in conjunction with the gaskets to fill the gaps created by the residual gasket that is safe for use upstream of the catalytic converter, which I just replaced.
4. Get a great suggestion from someone who knows what they're doing.