Hi..I have a datsun 1200cc B110 engine and need to hone out a little rust in the cylinder walls. How many .001 thousandths can I remove and still use original pistons? What size oversize pistons are available if I need to go that way?

For stock Pistons, it depends on how far honed it was in the first place

CLEARANCE, Piston to cylinder wall
A12: 0.0009-0.0017"

So time to measure the bore & the piston. If honing will make it more than 0.0017 inch clearance then oversize pistons are called for

Oversize pistons were available in +.25mm, +.50mm, +.75mm, +1.0mm, +1.25mm, +1.5mm

Better yet is a performance overbore using +3mm pistons (stock A14 piston). That changes the Cubic Centimeters from 1171 to 1270 cc. This gains more HP than upping the compression ratio. See A12 Overbore