I'll see if I can get to mine tomorrow to confirm, but the "Yamaha" graphics look like they are in the same position for both models, but with the "3s" having the swoop surrounding them.

This is an RT3 tank painted by Tim Rains. The "YAMAHA" is a decal. But he painted the "swoop" stripe. Incredible talent he has.

 

 

Will this help you? This is one of 2 tanks  I did by eye balling it. Good picture so you can see how it goes. I also have pictures of a original RT3 tank if needed. You will never get it perfect. Also it will depend on who's remanufacture decals your using as to how good they fit and look.  

  

Here is a different angle of it. My painter gave me some clear gel that is used to install graphics so you can move it around and get them right where you want them. Then use a credit card and squeezy them to get all the air bubbles and creases out. I think you can use soapy water to but the gel worked better.

After i installed all the graphics then he clear coated. Then i wet sanded and buffed to the shine i wanted. Be careful not to wet sand to much or you will go into the paint. 

 

Thanks for the pics skydancer46.  After sanding off the tank I discovered that one side of it actually had the YAMAHA embossed in the side so can use those measurements to position that decal.  Turns out that location matches the measurements I got from Dickie Towers for a DT2.  The swoop will be dictated somewhat I suppose by the decal itself since it has to follow the bottom edge of the tank.  But the top of it I suspect can end up just about anywhere.  If you have a minute, pull a measurement from the outside edge of the filler hole to the edge of the decal.  I would think that will dictate the rest of the decal's placement.  Now to get the tank painted!!

If using decals and aligning the lower line and fore/aft position of the curve by the lines on the tank, it seems to me that where upper part of the swoop ends up is going to be very dependent on the manufacture of the decal.   It's going to lay where it wants to...  not going to be able to move just the upper part much at all without wrinkling or tearing the decal. 

I knew you were going to asked that question. LoL! Unfortunately i don't own that bike anymore, But Member 1971DT250 on this forum has the bike. Contact him thru messaging, I am sure he would be more then happy to give you the measurements. Like Mark mentioned, where the top points end up is dependent on where you align the bottom portion on the graphics but you can move them a bit one way or the other. This will also depend on what graphics you use. Some are better then others as to how close to the originals they are. Have fun!

If you message me your email address I will try to forward you 5 pics of my original DT3 tank. It shows pretty much every reference point. I have quite a few of my bike too. If I can't post them from my phone,you'll have to wait a couple of weeks till I'm back at home.
Dave.