Your vibration person should be measuring phase angle as part of his/her vibration analysis to correlate shaft angular position to vibration events. Typically a phase reference marker is at TDC. Perhaps what is needed is the design information for crankshaft angle by piston position and valve opening/closing timing or crankshaft angle. I have found that many technicians who mostly do vibration surveys of balance of plant equipment have little or no experience with reciprocating machines (engines and compressors), and those folks with good engine/compressor testing and vibration experience are not well experienced with other machines. The reciprocating test instruments that often include vibration and ultrasound are not well adapted to vibration surveys of other rotating machines. It looks like a good opportunity for both parties to learn reciprocating vibration analysis!