You may want to give Jeff Glowacki at Sonic Craft a call. Looks like he loves these amps and will upgrade/repair them for you or sell parts kits if you want to do it yourself. He's a really nice and knowledgeable guy and I'll bet he could answer any questions you have about the differences between the two models.
http://www.soniccraft.com/upgrades/se40.htm
http://www.soniccraft.com/upgrades/se40.htm