Nice link. I was thinking about an adapter similar to that for the 700 FH shotgun I think that press-fit rim would be easier.
That "manual of cartridge conversions" book talks about different ways to adapt existing brass (or even brass tubing!) to fill those voids. The book has a big focus on obsolete cartridges, but I don't recall if it has anything for rims. I'll have to look at that.
Biggun the COTW book is "OK" but not anything I'd consider ground-breaking. You could probably find most of the info in that book in places like the accuratereloading forums. But the price was right - I'm glad I didn't pay full retail for it
One thing it has that *REALLY* piqued my interest is the .950 JDJ. Made from 20mm shells necked down to .95" and shoots a 3600 grain slug something around 2200 FPS. Something crazy like 20,000 ft/lbs energy! They were a limited run, but that has me thinking what else I can dow with those 20mm cartridges I saw for sale at the last GS. I think I need a big-bore dinosaur slug gun! I need to look more closely at that 700FH slug gun. But that's for a different disussion