So, its finished, and it works. After a long WhatsApp with the estimable Andyjr1515 I decided to at least postpone my original plan of shaving down the heel and do what Andy was suggesting, file down the frets where the strings are bottoming out. He reasoned that in filing down the frets, I'd not be doing anything as drastic as removing material from the heel of the neck, plus of course its easily reversible.
After messing about with the bass a bit I decided that every fret from 21-24 would have to be lowered, so I pretty much ground them down as far as I could. Its wasn't too bad a job only being the top few frets. Anyhow, I put the bass back together and its all pretty good. There are two buzzes on the neck now, but I that's more to do with my shoddy refret than anything else. It plays pretty nicely although the neck is a bit of a cricket bat- and thats after me slimming it down.
I decided to simply ignore the slope on the neck where it stands a couple of mil proud of the body just in front of the pickup. You have to look closely to see it and even when you do it looks like it could just be a raised centre block á la a Gibson T bird.
I'm delighted that this lovely and interesting old bass has been saved from the scrapheap. It will now sit in the corner of my living room as my noodling instrument.
Thanks everyone for the comments, advice and encouragement. Special thanks to Andy for the idea. Top quality basschatting!
A picture of the finished article below.