Hi Mitz,
First, I'll point out that "your" version is really the "revised" version. Mr. Weber almost always (if not always) adapts the original version using his own unique changes. You can find the original layout here:
http://www.ampwares.com/ffg/ Edit: Click on "Narrow Panel Bassman" on the left hand menu. Then scroll to the bottom and click on 5F6-A Chassis Layout.
You
can replace the WZ34 with a GZ34. The WZ34 is Mr. Weber's solid state "Copper Cap" that is used to replace a GZ34 tube. As long as there is a 5 Volt heater supply for the GZ34 (and in this case there is) you can use the GZ34.
As for the 12AX7's:
A 12AX7 = 12AX7B
A 12AY7 = 12AX7 but produces less gain, as does a 12AT7, a 12AU7 or even a 5751. It's all a matter of gain factor. You can read specifics here:
http://thetubestore.com/gainfactor.html Lastly, I'm not 100% sure about the fuse. I'm guessing it would be a slow blow based on my experience with my Vox amps but hopefully someone with a Bassman amp can chime in. Hope this helps.
Best of luck, Gerry (grod915)