Only suggestion's, Try some of these idea's...
1. Try Starting out with a Worksman or Husky frame Industrial Newspaperboy style frames are closest to those original Board Track Racer style frames.
2. Worksman frame is loosely based on 1910 Indian style frame except for the down tube.
3. You may want 2 remove the down tube & weld in a new looped or curved down tube from the head tube to the bottom bracket for the board track racer look.
4. Then you even could make a faux bottom for china girl motor will give a more original look of vintage engine.
5. Remember period correct bikes had matching paint on frame & wheels.
6. Front drum brake Sturmey-Archer better than most mfg's.
7.Torpedo style gas tank ( Indian ) or box style gas tank like ( Harley ).
8. No Fenders on Board Track Racer style bike, however the original bikes made for road use did have fenders.
9. Wheels The Husky Bicycle company has 11gage spokes on their wheels, Worksman Bicycle company only use's 12gage on their wheels.
10. Forks stay away from those monarch forks they are deadly with flawed welds.
Keep us posted as your build progress's i like to keep a build journal to write down all thoughts & idea's as your build progress's from its dob till it's completed also you can take a pic of bike a member has posted here print it out or a pic of an original bike from Pre WW I and draw on that pic your measurements using the worksman or husky frame as your template.
You can do it !!!
Look at these Builders bikes for inspiration or other ideas put on your creative thinking hat just like the original builders of Indian, Harley, Excelsior, Cyclone, Pope, remember they to were just bicycle builders who said i should put a motor on my bicycle.
Today's Builders who have gone down that same road are here in the Forum, like Motor Bike Mike of Simpson Motor Bikes builder of The Model 08, 09 & 10 Racers & although probably not a member of the forum George Whitney of Deuce Motor Bicycles who use's the Worksman Industrial Newspaper Boy bicycle in Burien, Washington.
Peace Crazy Horse...
P.S. All these builds except for Simpson Model 10 Racer built using worksman frame's start your build today & your build journal...