A Chevy 5.3 will bolt up to a 700R4 transmission, although one of the top bellhousing bolt holes will not line up.
And also to bolt a Chevy 5.3 LS engine to a 700R4 transmission, a special flexplate/spacer is also required and you also have to hook up a TV cable.
The flexplate and spacer, TV cable correction bracket and TV cable as well as crankshaft pilot spacer are all critical requirements for the 700R4 transmission to bolt up to Chevy 5.3 LS engine.
The Chevy 5.3 LS engine crankshaft is shorter than the older small block Chevy's crankshafts so you have to use a specialized conversion flexplate or even a flat flexplate with a crank spacer/adapter sleeve so that the torque converter spacing is correct.
And the 700R4 transmission also relies completely on a TV (Throttle Valve) cable that is set to line pressures and shift points.
So you also will need to use an aftermarket bracket to attach the TV cable to your 5.3 LS engine's throttle body.
And a small adapter sleeve is also needed in the back of your 5.3 LS engine's crankshaft to properly center the nose of the 700R4 torque converter.
Never drive the vehicle without properly adjusting your 700R4 TV (Throttle Valve) cable as incorrect pressure will burn up the 700R4 transmissions clutches in just a very short amount of time.
And also remember that 5 of the 6 main bellhousing bolts will line up and secure the Chevy 5.3 LS engine and 700R4 transmission tightly together, which is also very structurally safe for most applications.