I wonder what sort of results you would get if you copied onto transparency film to make a 5x4 negative?
A few years ago I copied some 10x8 glass negs to 5x4 by making an interpositive, the film I used was Kodak Gravure Positive 4135. As far as I remember the results were good but it was a very very slow process.
It may be interesting to copy onto 35mm to make projection transparencies, not sure what current film would be best for this, I got good results using the now discontinued Technical Pan film.
I just finished the series of prints I was doing from the old negs and some of them required as much as 80Y with Polycontrast to match the nice original prints. On grade 2, much of the detail would have been lost and the results would have been quite stark.
Unsharp masking to cut the contrast range back works on large format contacts as well as samller formats. This can help tame the igh contrast problems at times. For large negs I use ortho lith film developerd in a low contrast developer to get continous tone results, and develop by inspection under a red safelight, noting the time that I developed for to get the process close on the first try, and by timed adjustment on any subsequent tries.