BBDs are still being used in pedals. 10-20 mSec is long (IMO) for flanging, and a little short for proper chorus/double track, but my guess is the latter (chorus/ADT) is your application.
Check out the MN300x series... I think the 3005 may be marginally too long to make your shorter delays, but will deliver cleaner, wider response thanks to the high clock frequency. Something like the shorter 3001 will be running into audible clock frequencies at longer end of your desired delay range.
BBD analog shift registers are simple in concept. They require a two phase clock, to step an analog input voltage one clock cycle at a time from input to output.
For the shorter BBDs I have used simple cmos flip flops as clock drivers, while the longer delay chips have too much capacitance for that. I believe Panasonic also sells a dedicated clock driver.
While these are analog in/analog out devices, the audio is time sampled, so you need to consider anti-alias and anti-imaging filters to prevent birdies, and reconstruct the waveforms.
To modulate the clocks to provide texture to a chorus effect, you will need a simple voltage to frequency, or voltage to period convertor. It is generally simpler to generate a clock at 2x the needed clock, then divide that by 2 in a flip-flop to make perfect 50% duty cycle.
have fun... there are lots of guitar pedal schematics published on the WWW
JR
PS FWIW my old 1976 kit used MN3001, and one of my kit flangers was used on a popular recording (Heart's Barracuda).