I grew up restoring cars and trucks and specialized heavy equipment. I've had done and seen a lot of body work. The prep will always make or break a job.

You want to see metal doesn't have to be shiny or pit free but you want clean metal.

You don't want it to sit for very long after being cleaned as it oxidizes / rust again within a few hours.

Ultimately it comes down to you. You get what you put in. If it were me I would get that down to metal and prime and paint it.

I would probably pop the rear end out and have it sandblasted, at the minimum I would pressure wash, degrease wire brush, degrease wire brush pressure wash. Then finally hit any areas that need anymore attention. Final wipe down with rubbing alcohol or paint thinner something to remove any oils.

Use something like tractor enamel on parts like this because it's cheap and tough and usually comes in black and red. Thin the crap out of it and spray 2-3 times or more let dry between coats. Your goal is metal and paint with nothing in between.

Anything between paint and metal will fail and bubble up etc. Anybody who is worth a hoot knows that 90% of a paint job is prep work. Yes you can rattle can it as is, but it will look like it, and then worse as it fails. Then you'll be taking it back out to paint because the crappy job looks worse and stands out more than leaving it alone.

So if it were me or I was advising a client restoring a classic car worth 250k I would give the same advice, leave it alone or do it right. I did every job like my name was signed right on it, and thus would not do work that would make me look terrible.