If you have an existing material bucket, take some reference measurments off of it. The principle relationship that you are after is the measurement from the bottom (floor) of the bucket an the upper pocket of the quick attatch (where the upper wedge of the QA on the machine interfaces). If the rear walls of the two buckets are on different angles, you may need to alter the measurments to compensate.
Are you using a pre-fabbed QA plate? If so, you may want to simply mount this plate on the machine and drive it up to the bucket. Make sure that the surface that you are doing this on is flat and level (concrete or paved preferably), your tires are all equally sized and inflated, and your boom is in the fully lowered position. Tilt the QA with the bucket control to match the rear wall angle of your 4-1 bucket, ensure the bucket is centred on the QA adapter plate, and tack weld it in place. Re-check your measurements to ensure that the QA plate is straight and level on the bucket before finish welding it.
Not too scientific, but it should get you what you need.
Cheers,
SR