Thanks Arno, I think I done a lousy job of asking the question. So I have a 2048X texture sheet and a part made of multiple polygons. I want to use the top half of the texture sheet for half of this part at the first series of polygons then use the bottom half of the texture sheet for the remaining series of polygons of the same part.
I have only used FSDS2, so if FSDS3 does this differently the following does not apply.
The simplest way I have found to do this is to:
1. Select the part in question.
2. Go to Polygon Mode.
3. Select the polygons you want to use the 1st texture (the remaining polygons will use the 2nd texture). You can use the Mouse Select button to make this easier if useful.
4. Choose Part/Split Part.
5. Go back to Part Mode. The new part will already be selected, texture it using the first texture.
6. Select the original part.
7. Texture it using the second texture.
8. If needed (i.e. if you need to have smoothing between the two parts), select the two parts and choose Part/Join Selected. Then with Scale set at 0.01 in Project Properties, choose Part/Snap to Scale.
Now you have the part back in its original configuration, with each group of polygons textured using a different texture.
Thank you Tom!... I googled for hours to try and find this and I was just as lousy at finding the right words in Google as asking the question here. How do you get an answer when you don't know the question?
At any rate this is exactly what I was looking for and it is working perfect, the Part/Split Part was the extremely important part of this that I could not remember. Split it, texture it and re-join it, poof! top and bottom textures seamed side by side down the length of the part. FSDS 3.5.1 works the same as FSDS2. Thanks again!
Arno @ Jpfil I greatly appreciate your attempts to help as well, I was somewhat exasperated when reading your answers because I knew I wasn't asking the question very well.
A P.S. note here: I import my model parts from another CAD Program. If I imported the part as two separate parts I was getting a difference in sheen at the seam because the part was round and also had a twist. Using the method that Tom mentioned will give the even sheen in sim...