Hi Rod, just make sure you have a neutral setup on the OTK and that should be a good starting point, something like 55″ rear, 15mm of spacers each side on the front wheels, flat bar, neutral caster and medium axle. This is a very good start for most conditions. From there you can try changing the bar or caster in small increments.
I have no experience with the Birel wheels or other offsets on an OTK. However, the stock OTK wheels for that year (MXP) are better suited for low grip/rain situations whereas the stock wheels from 2015 and newer (MXJ) are a much better all around wheel. There are also the MXC wheels that many racers prefer, but they are quite pricey. If you do not have access to other OTK wheels to try, start with the neutral setup mentioned with your stock wheels, then try the Birel wheels, accounting for the different offsets by sliding the rear hubs in/out and see what you think. Good luck!