It was honestly quite underwhelming boosting a Marshall. The added lowend actually makes it cut less than a standard 808. The Asym is a silicon on one side and a germanium on the other. For boosting a Marshall, less clipping is better than more. And as for a rare opamp that can never be found, why obscure it? I used a 1983 JRC4558 on my last build, and I can’t see how a different opamp would be better in that circuit. Opamps differences are subtle to begin with. It was the pedal that drove my to build my take on that circuit. For what there going for used and touted as “designed to work on a Marshall” is disingenuous.