I did this very thing about 20 years ago in the engine in my car hauler.  I used standard chevy 283 pistons in my block bored to 3.875.  I had to machine retaining ring grooves in the wrist pin bores, the chevy used pressed in pins in the rods.  Had to shorten the pins to fit between the retaining rings.  The Ford rods had to be honed to chevy wrist pin size, and the pistons had to be cut on the top so they wouldn't pop out of the bores at TDC.  There still were 4 shallow valve reliefs remaining in each piston, which lowered the compression ratio.  There was a sizeable difference in piston weight, which caused my engine balancer to work a little harder on it.  Would I do it again?  NO!  I'd have custom pistons made if I had to have that bore size, but I would just start with another block and bore it to an available oversize piston.

John - "The Hoosier Hurricane"