I have a 76 shovelhead with a cracked front jug, I have a spare set of jugs, pistons and rings from another 76 shovelhead, can I just bolt them on
Have the cylinders torqued up in torque plates and check for a true bore; if the bore is true then check piston to cylinder fitment; if close enough buy a new set of rings, have the cylinders lightly honed just to break any glaze on the walls; clean them up, assemble and off you go.
If cylinder bores are not true, they will need to be honed to fit a set of .010" OS pistons.
Torque plates are not necessary for a Shovelhead. Cylinder base bolts to case, heads bolt to cyl., so there's no sandwich effect, plus cylinders are steel.