I have both the 90 and 91 FSR engines and they are great engines. I especially like them in the TF Gold series warbirds where the weight of them eliminates the need for useless lead up front to balance. If you gotta carry weight up front for balance then it might as well be part of the powerplant.
I have found over the years these engines run best on 15% Omega for me anyway. Because they rev pretty high I use wood props either TF or Zinger 14x 6.
They are much quieter than Master Airscrew and the performance is better as there is less flex at the tips. APC props wont work on these engines as the crankshaft is too short to handle the fatter APC hub and then the prop nut is not fully on unless you scrap the stock OS washer and use something thinner. Even then I don't like the fact that the prop nut is not fully threaded on.
As for plugs I use the OS #8. They do a good job and last a longtime. Back in the day the old Fox idle bar plugs also did a good job but they didn't seem to last as long.
Finally you don't need the pin in the thrust washer unless you enjoy drilling holes in the back of the prop. I haven't used mine in years. If you use the wood prop with the supplied prop washer the nut will fully seat and when tightened properly there should be no problem.
Good luck with your motor - you will like it i am sure.
ByronF