If you want to run regular 6374 motors, you want to use these. You will get 149mm of space for the motors between mounts. Adjust with 0.5mm washers that comes with the crossbar if needed. Let’s say you need 152mm between motor plates. You then need this spacer kit and use all 6 of the 0.5mm washers included. If you need more washers, just tell me.
If you need even more space, consider combining with 10mm spacers for 169mm between mounts.
2x white M8 15mm nylon spacers for extending crossbar length. 30mm long screws included.