How much metal are you planning to take out? Unless you plan to redesign the head there I don't see why you want to bother cutting one into sections.

Would that be a realistic way to salvage the guides without having to replace them outright?

In a word...... Yes.

My only concern would be the potential for having problems reaming out the original guides by having the reamer stick, or not cut to the proper size.

The reamers are well over $100, so if it screws one up...... It would have been cheaper to just replace the guides.

Thats a pretty penney.

And that doesn't include the needed seat bushings($280) that are used with the boring tool.

And I can also tell you from experience, that the broaching tools don't do a very good job of sizing the liners when they're installed into bronze guides because the original guide material doesn't provide a rigid enough backing.

So, you usually end up needing to use a rigid hone to get them sized properly.........that's another tool that's about $500(just checked......over $700 now).

Then the seats need to be re-cut....... and that gets done on a $23,000 tool.

and, you need another separate one for 3/8" valves, and 5/16 valves,and you should really have a stem height gauge, another $200, and then a concentricity gauge, another $200, and maybe a split ball gauge for sizing the liners, or a valve stem comparator, about $500 on the low end to $1200 for the Sunnen and then, you need a $1,000 cutter kit, if your using the 3D type tooling, then you need the replacement cutters, that went from about $30 at Sunnen, to $90 each , and then if you want a diamond hone, thats another almost $1200 for the kit., and then you need 5/16, 11/32 and 3/8" liners, another couple hundred...and if you like touching up the machine cut seats with a stone, thats a $2500 seat grinding kit...and the list and costs, go on, and on and on....and when shops charge $200-$250 for a valve job, and people think that is " high"......just saying...lol

Not to mention there is usually a little learning curve that happens before you really get consistent, high quality results.
Like with many things....... It takes practice.

In the end........ If one is determined to use heads with a history of guide problems due to inferior parts installed at the factory........ It's generally better in the long run to just pay someone who has already made the investment in the tooling to swap the guides out for you, and recut the seats.