You do not need to run digital servos in this 60-90 size plane.
If I would build it (that's what I have in my Showflyer), I would put in it :
JR 4131 on ailerons and elevator, and a 2721 (faster) or 4721 on rudder.
This is enough servo for it. Another way to save some servo money is going with Hitecs. 625MG's instead of JR 4131's and a 645MG instead of JR 2721 or 4721 ! Any standard size servo for the throttle will work fine. I use JR 537's.
Make sure you keep everything light and use a light receiver (JR Slimline 700 or Hitec 555), and a light 6V battery pack. The 6V gives you top servo speed and performance. The 6V 1650 NIMH pack from Batteries America or RadicalRC use AA size Batteries. Batteries America now have a 2000 pack with AA size batteries.
Light weight and therefore low wing loading is the key to optimal performance of these 3D machines.
Just my $0.02