Tim
I have 12 Handi's and the base on all are the same. Three hole in base to mount to barrel as You know.
This new 10 Ga barrel is set up for intermediate eye relief scope. It has four base mounting screws. Each set ( 2 screws ) is half inch apart, center to center. First set is 7 and 3/4 inches from breech of barrel . second set at 10 & 3/4 inches . 3 inch spread between the two sets of screws.
I will call H&R in the morning.
I'll let you know what I find out.
Eddie