Time to make use of those MN3207's you have laying around. I have made this layout against the factory schematic available here: https://www.hobby-hour.com/electronics/s/boss-bf2-flanger.php
I have substituted some components for more common/popular substitutes but have also listed the original parts if you like to use them. Check your transistor pinouts if you use anything other than the susbstitutes I have used in the layout as the may be need twisting. Sorry if you don't like standing resistors but I wanted to make sure it fit in a 1590BB. I don't mind standing resistors at all, a lot of other components are standing anyhow. Ah, thanks groovechampion, I have now fixed that typo, MN3204/MN3207, same pinout, grab the updated layout.