The tubes of course don't care what frequency they distort
I´m too lazy to search for the original schematic. But what I see is that your 5534 lacks the compensation cap. And IIRC R35 was much lower in later revisions of the 250.
SW-pin3 connects to the other side of R31 (only one half of the dual rev-log pot is shorted out, the 3k3 R31 remains in circuit) ...
IIRC additional compensation cap between pins 5/8 for the NE5534 shouldn't be needed.You are aware, the boost/cut pot is missing the center tap connection ? (pot is at least a 4-pin device)