I have twin 4.3 Alpha 1's on my 88 Chris Craft 290. I pulled the drives off this winter and went through both of them. One drive has no shims behind the carrier. Is that common? Because all gears, bearings and races looked good I just replaced oil seals, o rings and gaskets. I have a mercruiser service manual #6 . I have all special tools except except preload tool to check backlash.Do I have to check backlash before putting these drives back in service? Both drives ran perfect all summer. The only reason I tore them down is because they are old. Lastly when installing the carrier on the other drive with shims, which one goes in first, the black split one or the others. Thank you in advance for any feedback. This is my first time in my life I have ever posted a question on the internet.