Forget about the green completely. A good HSS grinding wheel on one side, and the diamond on the other would be good. But be aware that most brazed carbide grinding is done on a flat side wheel such as the 6A (IIRC). The hollow grind of a peripheral wheel is not desirable on carbide, though it is on HSS. Also note that you'll need to keep grinding of steel on the diamond to an absolute minimum or it will ruin the wheel. So if you start getting close to the steel on a brazed bit, you'll need to clearance just enough so that it doesn't eat (literally) your diamond.
And 6" is tough to get good wheels for, though with searching it's possible, but they tend to cost more. The most common size (by far) for good wheels is 7", because that's the size used by the vast majority of smaller surface grinders and tool grinders. But, those grinders use hubs, so the wheels have 1.25" holes, and making an adapter hub is an excellent early lathe task. But that doesn't help you on the 6" grinder. I use a 7" grinder, so I can't help you much there, though I know it's been done (or rather I've seen posts). As to the 42A, you'll have to look that up, I'm not familiar with that designation's application. Harold and others on Chaski are a HUGE wealth of information regarding grinding, and you may find the answer to most of your questions in the threads I mentioned. If not, I'm sure they will be able to provide better input that I can. I basically learned what I needed to make mine work for me, but I don't have the broad general (real world on the job) knowledge they have.
