stripped intake manifold threads in cylinder head

[TMat]

I have a big block chevy with aluminum heads. Two of the threads for the intake manifold bolts have stripped that are in the heads. I was going to drill and put new inserts with the heads on the block, but these are not blind holes. Is it advisable to do this with the heads on the block or should they be pulled off?

Any help would be appreciated

thanks

[xplane]

If they are not blind, i assume they are open to the lifter valley? If that is the case they will definetely have to be removed to repair.

[TMat]

I believe they go to the coolant passage, not sure.