68 hemi aluminum waterpump housing.

I picked up a race hemi aluminum water pump housing and have been working on getting it
cleaned up to go on my engine.
I got this housing from Adam Adamic several years back if anyone was curious of its origin.
His father Al ran a BO29 in ssba named "Al's Toy" out of Ohio when new.

Anyway being a race part it never saw antifreeze and is coated with rust stains and some corrosion on the inside passages. I have been cleaning what I can reach with a small brush
and some rust remover. (naval jelly)
This has worked pretty well where I can reach but would like to clean the areas I can't reach also.
I was hoping someone knows of something I can pour in or soak and rinse out that will work on the rust stains. The naval jelly requires a lot of scrubbing and doesn't work by soaking alone.
I am trying to avoid the blasting method if possible. Any ideas?
I will try to get a good picture of the rust problem up.