So my U-joints have gotten noisy, I am going to pull the drives to fix them and I have a question about the parts I will need.

Is it just the cross and bearing (16) that need to be changed or do the yokes (15, 17, 18) get damaged also. I am assuming that I can change the cross and bearing without taking the driveshaft off of the drive.

Are you sure the noise is from the ujoints? Could be the gimbal bearings in the transom assembly.. If the caps on the cross bearings are a tight fit in the yoke then the yokes are good. Unless you see some other damage to them. Generally, only the cross bearings are replaced.
hope that helps.
Dick

While you are inspecting things; take a mic. and check the O.D. on the input spline shaft, at the area the gimbal bearing rides. I have found wear and taper in the area, that will cause noise.

I am planning on changing the gimbal bearings at the same time just to be sure. I'm pretty sure I f'd up the u-joints trying to power off a sandbar, being a jacka$$. The boat runs fine I don't feel any vibration but when it is out of the water being flushed they make a lot more noise than they did before the sandbar event. Also the noise changes as I trim up and down or turn side to side while flushing. Does that give any insight into which part is the problem? Thanks for the advice.

You are referring to part number 18 correct? I will check that also, thanks!

Yes, Part# 18

turned out the gimbal bearing was the source of all the racket, u-joints were in perfect condition, and the alignment was perfect also.

Good to hear you found the problem!

MER I have also seen this but the problem seems to relate to the older Gimbal Bearing was installed in the 1998 and above assemblies. Have you seen this using the correct gimbal bearing app on top of ? The older GB is a lot cheaper so hence a lot of end users buy it. For example many people and shops will use Sierra's 18-2100 (link belt) gimbal bearing for 1998 & up Mercruiser apps. Wrong bearing.