I will second the red kote route
I just did two /2 tanks with it and one was a victim of poor preparation and por-15 that either didn't stick or had not held up. Unfortunately the best way to get the residual stuff out is time, heat and then a lot of shaking and rinsing.
You might get lucky if you put the tank under some heat lamps for a few hours to get the liner crispy and brittle and then do the shake and rinse routine.
Getting back to the Red Kote stuff. You have to mask off the outside of the tank really really good before you get the stuff or the MEK near your paint otherwise it will come right off. The Red Kote will seal up any of the little tiny chunks of the old liner that doesn't flush out or is partially attached.
The inside of the tank looks to be a mess and you may want to consider the radiator shop/boiling it out route and then repaint the tank. If there's no body work to be done a competent painter can give you a factory finish for a lot less than you would have in time and aggravation and possibly damaging the paint anyway.