Ah yes, after the psi4-dev installation, need to replace the am6 libint that that brings with an am8 libint through conda install libint am8 -c psi4/label/dev. Check that [am8] now appears in conda list. Then run the psi4-path-advisor line (removing the incomplete objdir/ from the previous build beforehand). Then build. Without building libint internally (which indeed can take several hours), psi4 builds in a few minutes and w/i 30 min on travis-ci, so shouldn’t take too long.
@jturney took another look, and drop in replacement is tricky b/c array dims are expected to be available at compile-time. If the above doesn’t work for you, I’ll build a psi4+am8 conda package you can use. I won’t build it regularly, but hopefully you and others aren’t at the intersection of high AM and bleeding-edge features.