> is it safe to ask them to blast the insides of the exhaust
> and intake ports?
Why ?... what do you think you are gonna gain by it ?
Not much of anything ... just get an old metal butter knife and scrape out any carbon... the sandblasting isn't gonna gain anything.
annnnd... if you want them NOT to sandblast any area... YOU ...had better tape it off... (normal sandblasting won't eat thru duct tape).
What if they don't understand your 'instructions'... and sandblast the wrong surfaces ?
... the only time I have had people sanblast cylinders or heads was rto get rid of baked on dirt and old paint... (on the OUTSIDE only).
I wouldn't let them touch any gasket surface ... or the 'inside' of either part.