I have two JC Higgins Model 50 rifles (with FN Mauser 98 actions). They both have the wide rear scope base hole spacing of ~ 0.86".
I did some research, and found out that Warne Manufacturing makes a steel "Maxima" base that will fit. I spoke to Jerry Langford (Technical Support) at Warne Manufacturing, and he told me that it was not a popular item (not even listed on their reference chart), but they do have it. They are made in the USA.
The rear base is item "M831." The matching front base is "M902." The bases are $12.95/ea (~ $26/pair) + shipping ($7) direct from Warne Manufacturing. Jerry said it would be unlikely to find this base listed at one of their current dealers (he was right, I looked). Dealers had the M830 or M832 rear base version, which has the 0.50" hole spacing-but not the wide hole spacing (I looked).
I bought two pairs directly from Jerry at Warne Manufacturing. They fit perfectly.
For those who have this classic rifle with wide rear scope base hole spacing, Here's a quality, nicely priced scope base option. They are set up to receiver "Weaver style" scope rings. Highly recommended.
Thank you Jerry at Warne Manufacturing.
Warne Maxima scope base reference chart Jerry Lanford's email: jerry
warnescopemounts.com