9015 Motor to PG71 Gearbox

We’re having some issues attaching a 9015 motor to a PG71 gearbox, which was previously attached to an RS775. The 9015 shaft is longer than that of the RS775, making it impossible to attach the 9015 flush to the PG71 (as the 9015 motor’s shaft is blocked by the internal gears of the PG71):

The bottom picture shows the 9015; the top the RS775.

Since the CAD drawings of the PG71 do not contain the individual parts of the PG71, and the 9015 CAD drawing included depicts a motor identical to ours, (am-0912), we can’t tell how it all fits together.

Do we need to cut down the shaft of the 9015/add spacers between the 9015 and PG71/is there something we’re missing?

I believe there is a hardware kit to mount the 9015 motor to the pg71 from andymark.