I have a possible 12.7 that had a full inframe I might be able to get if its the right series and it's had no miles on it since finished. Don't think it would be very expensive. We would just have to make sure it would work !!
Just my own opinion, but you have done a lot of work on the ole girl and you know what you have. A pretty dependable truck. I would would do a full inframe on it and go with it.