The suffix matters, the CS800b schematic I have has no op amps at all. The CS800s schematic won't tell you what U104 is,. but U101,102, U103 are 4560's same pinout as your TL072n. U104 is a 13080 which a part number from merged out Harris. It is a transconductance amplifier with a weird pinout, and weird characteristics that make it unique. For the DDT to work and keep the speaker coils from frying from distorted guitar sounds, You need one. A CA3080 from merged out RCA is probably the same thing, since it has the same pinout. I bought some from Jameco in Calif. I haven't really tested it to see if it works, I don't have a guitar or crunch pedals. The circuit works without it, all except for the DDT speaker protection. Enzo keeps saying how nice the Peavey parts dept is, but you do have to talk to them on the phone, they don't sell via the internet. The other unique parts I know of are the J174 jfet (just went 2000 minimum buy at newark.com) and the dual bias diode embedded in the heat sink. Output relays are unique, of course.