V -block was my thought at first glance too … but the picture looks like the channels aren’t machined to hold a clamp and the cuts that would be "V" aren’t deep enough to hold much of anything. Important surfaces are the flats, imo
Dunno what they’re for … but with 2 in 11/16 x 13/16 x 4" … might be handy as super-duty parallel bars, especially in a 1" deep vise ,,, ?