What the heck is (was) this?

[Pete O]

(08-31-2018, 12:54 AM)awemawson Wrote: Cut it into slices and surface grind top and bottom to make several sets of parallels

I think I'd rather find an application that takes advantage of the fact that it is a great big chunk. Such as an inclinable fixture plate, either with t-slots or lots-o-holes.
Still looking for a thick piece of plate for the frankenmill part, I might have to make my first foray into iron melting and cast the part if I can't find a billet big enough.