You will need a bucket, gallon of white vinegar and quart of lemon juice. Depending on the bucket size, mix 2 parts vinegar to 1 part lemon juice. Soak part along as needed. Pull part from time to time and scrub with small tooth brush size wire brush. Keep repeating until you are satisfied clean enough to paint. Wash, dry and get ready to apply paint as flash rust will appear as soon as the part is dry. Took about 6 hrs to soak and come clean. Going to finish off with wire wheel. Before and after, you can see flash rust .

Looks good as new, what will you be using for a primer?

Nice, Mark. I have a collection of those that could use this treatment. Some that work better than others

Although I think you are making it more difficult than needed
Apple cider vinegar (min 5% acidity) toss um in undiluted for a day or two.
Pull out & rinse using a brush to remove rust sediment (will come right off).
Dunk in a bath of water & baking soda to neutralize
I go to the added step and blast them & powder coat the outsides otherwise theyll rust in no time.

Or, just drop them in a blast cabinet?

Going to use high temp primer and paint. Blast cabinet method is ok if you are going to powder coat because paint needs rough surface to adhere. Did not have loads of time in job, let the bucket solution do the work. Maybe 5 min in clean up each brushing.

Memory is old but think there's a cork gasket on that and it seems like 914rubber had those at one time. miscellaneous thought

The best rust remover I have used is Krud Kutter The Must For Rust. Soak parts overnight. It removes rust and paint and etches the metal for paint.

Final result

Very nice Mark, thanks for sharing. Mark

If you want to speed up the process hameat the vinegar to near boiling. Smelly but works fast.

I REALLY like Evaporust. Works extremely well with overnight soaking, and seems to be very safe for any plastic bits that can't be detached. But it will remove paint (for good or bad).

https://www.evapo-rust.com/evapo-rust/

Turned out nice!