Stupid question; would you sandblast cast iron manifolds before or after having the matting surfaces milled to ensure a flat surface or does it really matter?

I'm getting ready to redo my exhaust manifolds for my 69 Road Runner and have been wondering what step would be best to do first. Do you think the sand could cause any issues on the surfaces after they've been milled?

Personally, I would blast and then mill/planed. However, if you chose to do it the other way, sand blasting shouldn't hurt it.

Just went to pick up my manifolds today and the shop hot tanked them before they worked on them so; I don't even have to worry about sandblasting anymore.

The shop dog bit my hand 5 seconds after I handed over my debit card and opened a couple of my fingers up; the owner handed me my card right back and said that the work was on the house.

The bill was only $62 for hot tanking, belt sanding the mounting surfaces and welding the heat riser holes up; I would have been happy to pay that. I tried to hand the card back to him but he would not take it. I understand because some would sue or something stupid like that but my fingers were just skinned up and I'm a dog person.

I stayed and talked with the owner for 5 or so minutes; he had his late 60's Camaro race car in their and we talked about some other projects he had around there too. Come to find out our dads worked with each other for 20 some years.

I've had this guy do some work for me in the past and so have my friends; he does a good job. If anyone needs any machine work done I would recommend Phillips Racing Engines in Grove City, OH.

I would say it doesn't matter either way, you can always put duct tape or masking tape on the machine surface to protect it from the blaster.

I've etched glass in a sand blaster using masking tape as the pattern template. Blaster didnt touch the masking tape.