After building my valvecaster, liking it, and realising I don't have a tremolo. I went ahead and made this stripboard layout for the vibracaster LFO taken from Rick's vibratone schematic. Pot connections may need reversing.

Verified and working well.
I'm running it off the regulated 12.6v heater supply. My valvecaster uses a 12at7 and runs on 21v, it also worked well wired to this. Had a bit of ticking which was removed by putting a 220uf cap across the + and gnd. The 8k2 resistor may need changing if yours runs on other voltages. 27k gives me a nice range from subtle wobble to chopping. 47k is stock for 12v.
Added a flashing rate LED. Based on Taylor's rather artistic post here.
http://www.diystompboxes.com/smfforum/index.php?topic=79078.msg657184#msg657184...and added to the vibracaster schem like so.

I've put the LED on the emitter as the non inverted signal makes it flash clearer. Flashes on rather than flashing off.
I'd be interested to know if there should be any reason not to do it this way.
I tested it with various gain settings and checked with a scope. Works well and doesn't affect the sound or LFO waveform, not a tick or bump to be seen.