Motorcycle Repair: FORK TUBES, fork tubes, triple trees

Question
IM BUILDING A RIDGID FRAME WITH 38DEG RAKE 4 INCH DOWN STRECH 1.5 INCH BACK 0DEGREE TREES A 21INCH FRONT TIRE AND A 16 INCH 200 REAR TIRE.I HAVE STOCK 1979 FXS TUBES 33 INCHES. COULD YOU GIVE ME ABOUT WHAT LENGHT OVERSIZE TUBES THAT WOULD GIVE THE FRAME A STRAIGHT LOOK. I WILL DEAL WITH TRAIL WITH RAKED TRIPLE TREES LATER. THANK YOU.

Answer
There we a few factors that you left out, but I will tell the easy way to do your figuring.
First, installt the rear wheel with the tire. Block up the frame at the angle you want it to be. Now measure at the angle of the neck down to where the front tire will sit. You will probably need a buddy to help. Have him either hold the front tire, or if you dont have a front tire yet, then measure from the floor up half the distance of the tire. The measurement from the neck to the center of where the front axle is is the length of forks you need. Standard length forks are around 31.5", so take your measurement, minus the 31.5" and that will tell you how much more tube you need.
Good luck and happy riding
Mike