If you look at a ported exhaust port, you'll see that even the CNC'd ported heads like AFRs will leave the guide intact. Do a websearch to see what those look like. They'll shape the guide to a teardrop and blend that with the roof of the port. Why? You need that part of the guide contact to help cool the valve stem.
Most of the area the pics are showing as ported-away is the thermactor bump. You really need to see views down the port and down into the valve bowl area to better get the idea. this DIY head porting gives you a better idea of what to port, and also the area NOT to port. Read all of the side-bars. Bad porting can actually hurt flow. Yes, I realize that the examples they use are E7TE and GT40Ps, but the information is valid for most OEM Ford heads.
Good points Milo - there are various factors for different heads that are positive or negative for flow. Get a performance book that covers your heads specifically and you can glean very good info and learn from others mistakes. Sometimes having a bump in the right place actually helps flow dramatically! It's an art - no doubt. Many heads get trashed by the removal of to much material! Practice on a cheapy bad set to get the feel
To answer your question... IMHO your best bet is to not even touch the guide with a grinder. If you're a first time porter and you're gonna do much more than just "clean 'em up", you really need to flow them to establish a baseline and any gauge improvements after porting. Trying to hog them out 'cause it looks slick is rolling the dice and you'll likely do more harm than good. There are places to grind and places NOT to grind. There are formulas for intake vs exaust port size and other aspects that you want to know or at least have a clue about before you start grinding. Violate that math by very much and you'll likely have wasted your time and your heads. You can build your own flow bench out of a shop vac and some other stuff but my recommendation is to find someone with a Superflow or other quality flow bench and pay the man. You'll get truer numbers and might even get some good info after your first visit. It doesn't hit the wallet that hard and you might find that the guy's price for porting isn't that bad either. What ever the average guy will do in his garage will not equal the flow a pro with a flow bench will give you. Like a buddy of mine likes to say,... it's hard to beat a man at his own game.
I'd also watch out for the coolant passage right above the top yellow line. Could hit water depending on how large it is vs the section we see in your pics. Very good advice ^^^^ getting a bone yard head to practice on. Are those pics the actual heads you want to use?