Oh that is a beaut!! I used to lust after those puppies man. I'd play 'em in the store I worked at and just drool.
The Echoplex was the king daddy but the Watkins/WEM was awesome also. Nothing like tape delay man.
Today if you want this type deal you have to turn to the Fulltone TTE Tube Tape Echo which will put you back about 1200 bones.
Interestingly, the Echoplex
model in Eleven Rack along with the expression pedal is a SUPER sounding modeled alternative.
I also have the Xotic Effects EP Booster which is a circuit designed after the preamp circuit in an Echoplex. It really warms up the tone. Great for single coils.
Here is a nice article on Echoplex's.
http://www.in2guitar.com/echoplex.html