I quick glance will tell you.
The 460 had a separate timing case where the 400 the timing case was cast as the front of the engine block.
You can count the valve cover bolts or note the thermostat placement, but for me it's easiest to look for the seam or gasket on the front of the block.
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.