W124 Can't figure out fuel pressure drop.

[Abstemious]

89 300TE m103. Car has sat for a good while for new head. Everything installed now but having issue with my FP immediately dropping from 80+ psi to +/- 27 psi. I put in new check valves on my FP's and have the accumulator line clamped, also new FP regulator... and still getting this immediate drop in FP measured at top chamber port. Also, I have my fuel lines off and am not loosing fuel out the top of the FD through the FI holes. What else could be going on besides the accumulator and the check valves? Are bad check valves out of the box reasonable possibility? Can these valves be checked manually off the car ? Any ideas here much appreciated.