I'm trying to see if a valve body out of a later trans with part-throttle kickdown is in decent shape. I can't get the 2-3 shift valve to pass through the final orifice in the valve body - it gets too tight to push through as it starts becoming flush to the outside.

The whole VB is a bit clutch-dusty, but hitting the area with brake cleaner and then some new ATF didn't seem to help. I'm wary of using much force or direct heat for fear of messing up the whole casting. Do I need to clean up the orifice at the edge of the valve body more? Heat up the whole thing in the oven or something? I can't figure it out.

Use a punch to drive it out; it might just be a varnish ridge that prevents the valve from coming out but if the valve shaves aluminum as it comes out, clean up the casting and see if the valve moves freely in its bore after cleaning.

pour some carb soup on it & let it set for awhile. If it is a metal interference issue I ain't sure how to proceed but give it a good soaking & cross your fingers.

i use several different shape machinist picks to get stubborn valve body pistons out. i don't like to see them shave material from the bore of the casting though. that can cause internal leaks if bad enough, in my opinion. soak in lacquer thinner, carb soup, mineral spirits, etc. for a while, and that should soften up the gunk build up.