What do you guys recommend?

 

Either, I prefer to rough out a port first, because if I screw something up then I can throw away the housing with little investment in it and grab another. I do this because I enjoy experimenting and own plenty of spares. But you can go either way as long as you check that your timing is where you wanted it when it's all said and done.

 

Do it before. that way if the grinder skips a little bit and scores teh housing slightly that will likely get polished out when its resurfaced.

CJG

 

When I port, I outline the port dimensions with tape for a few inches, so if I do slip, it doesn't nick the housing. I am also very careful.

 

You can do it before or after. Either way you have to be careful. Every hole (except the oil metering)should be masked off in a way that allows the plating to slightly go into the hole.
You neen to "clean" the ridge very slowly with a extra fine grit stone. Be sure that the rotation of the stoneis going toward the edge of the hole or parallel.
If not you may chip the coating and give a "flaking" effect.

Porting beforehand will allow for some "minor" grind "dings" in areas that you may have accidently scuffed. By the time the housing is prepped for resurfacing those dings will be gone.
If you ding it afterwards, oh well