These are older items (before Genesis), and they use the Poser file structure. The are stored in a Poser Runtime folder, and nearly all clothing, buildings, cars, people etc, are known as Figures. The V4 bodysuit will be in Figures as well, that is correct.
The Materials for the Bodysuit are applied using what is known as a ‘MAT Pose’, in other words, a Pose file which does not alter the figure’s pose, but does change the figure’s material.
Load the V4 character first, then load the V4 Bodysuit. Select the Bodysuit in the Scene tab, go to the Parameters tab, and select the ‘Fit To’ option, and fit it to V4. Then you can go to the Pose folder to find Diving Suit texture that you want to use. Make sure that the Bodysuit (not V4) is selected in the Scene tab, and then apply the Diving Suit texture that you want from the Pose folder.
All of this is done in the Content Library tab, Poser Formats > My Library > Figures.
I only have the bodysuit, and I have applied it to V4, and used the Fit To option as well. I don’t have the Diving Suit, but the bodysuit fits V4 very well. See image below:
Click thumbnail to see full-size image