I just went through a very similar process. I bought a bunch of old Mifer (Spanish) gouges from craigslist. I tried to bevel them on the stones but the steel was way too hard and thick and just took too long. After about an hour on one chisel I decided to give the grinder a go. You can do nearly the same thing by hand but it will just take a lot longer. For your time, it is probably worth it to spend $50 bucks on a 6" bench grinder. Most come with a wheel on each side (you won't need the course one) and you can replace it with a 6" cloth or whatever type of honing wheel. This makes rehoning every 15-20 minutes much quicker when carving.
Thankfully they did not have hardly any surface rust. Red rust is what to watch out for as it can mean deeper pits in the blade than you might suspect. In this case you can take off metal from both sides until hopefully you find a clean center from a stone grinder. I had to do this to a old planer blade which was gifted to me recently and turned it into a double-bevel chisel.
If you are free of surface rust I suggest using a bench grinder to set the initial bevel. Hold the blade sideways and turn the handle as if it was a screwdriver while gently touching it to the grinder. Be patient. Go slow. Dip the tip in water constantly. If you burn the metal (heat generated due to friction) it will change colors. The temper is lost, and you need to grind out all the way.
Like the image below:
The goal is for after polishing for the bevel to be FLAT from the start of the bevel to the cutting edge (the gouge will obviously have a curve to it, but this should be from one cutting-end/bevel to the other, not from the start of the bevel to the blade). This means light reflected will have minimal bend, and be more like a flat mirror. The more bend the reflection has, the more the bevel was bent towards the edge, giving a more cannel (or Moran) bevel to the blade. While this Moran edge can be desired in certain situations, typically when done unintentionally (aka on accident due to poor flat bevel sharpening) the quality is not so good.
I have attempted to show it below:
I attached a picture showing the bevels on the gouges I sharpened. They are not perfectly flat, but they are acceptable (to me):
You can put sharpie all over the bevel to make it really obvious where you are hitting. Frankly it will be obvious anyway since the grinder leaves fairly course markings. Afterwards hit it with honing compound on either a wheel or strop for a few minutes, alternating sides until the small wire burr at the end of the blade comes off.
I will sometimes grind the end flush if the gouge is way off, leaving a very thick end. Then as I grind (as shown in the image above) I will check the thickness of this edge constantly to make sure I am grinding evenly along the radius of the gouge. The goal is to cut through the thick dull spot on all parts of the blade simultaneously, which implies an even grind. As the tip gets thinner and thinner it gets easier and easier to burn. Dip it in water every 1-2s of grind, seriously!! It sucks to burn the metal right at the end of a otherwise good bevel.
PSA: The bevels I ground on the wheel gave me a bad skin reaction all over my hands back and around my mouth where the respirator was (weird). I don't know if it was the vanadium steel or what. But just a heads up use long sleeves and good ventilation.