Looks like the electrosmash tubescreamer circuit with shifted filter points (high-pass of ~600Hz, low-pass ~1500Hz).
You could easily build this with the little green scream machine pcb and about 5 part substitutions. You'd need a clipping diode switch but those are easy to add externally. Or you could use the JHS Moonshine pcb and you'll have a charge pumped version of that pedal.
A lot of the differences in that circuit and the original tube screamer are simply because of availability (470k vs 510k to bias the transistor stages, the 25k pot instead of 20k). The significant ones are in the feedback look that set the gain and filter values.