I thought a small and simple phaser would be another good addition and so the Phase 45 is the automatic choice to remain 1590B friendly. For the best results the JFETs need to be matched so you can either swap and change to select the pair that give the best sound, or measure them using a method like this one so you know they are a close match.
Info from MXR about their currently available 75 Vintage Phase 45:
The ’75 Vintage Phase 45 reissue from the MXR Custom Shop reproduces the rare little brother of the Phase 90 to exacting specifications. With two stages of phasing, the Phase 45 offers up its subtle and musical voice via hand-matched FETs and hand-wired circuit board. Authentic tried and true components and hardware such as a Carling switch, CTS pot and Switchcraft jacks. Texture your tone without over powering your sound with the limited-edition ’75 Vintage Phase 45.
Geiri’s video of his build:
