The vintage AC30's had a few problems with how they were made, and shorting one side of the heater to ground is one of them. Some of the older Fenders like my 1956 5E3 are wired this way also, and it is simpler to wire it that way but results in more hum every time. You would want to wire up the heaters like Fender did it in their blackface amps as it will result is less hum.
There are lots of Fender kits out there but AC30 kits are not as easy to find, especially something that is the same as a vintage one. There are many reasons for this, but a couple are that AC30's were not as widespread as Fenders; AC30's had some issues with how they were made that require changes to get better performance such as the heater connection as mentioned above; the chassis arrangement is unique to Voxes; the circuit is quite complicated when you also have the tremolo and vibrato circuits included.
I would suggest that you get the Vox Amplifiers: The JMI Years book by Jim Elyea. It has everything you ever wanted to know about vintage Voxes including schematics, histoary, parts used etc. Here is a description of the book >>
http://www.premierguitar.com/articles/Vox_Amplifiers_The_JMI_Years. You can do a search at Amazon or elsewhere to buy it. It is an expensive book but it is HUGE and is the best book anyone has ever done about an amp company. They have all the JMI era Vox amps in there too, not just AC30's.
The signal caps used in many of the originals, and in the picture you linked (gold with a red stripe) are Wima Tropylfols. I have some that I got at surplus places in 0.22uF and 0.1uF values, but they are hard to find for other values at surplus places. You can find them on ebay from time to time but they are not cheap. They are good quality and good sounding caps though, but any modern cap such as a Sozo, Mallory 150, etc., are likely as good or better.
Greg
