If you don't know what the delivery valves are, that is a big problem. Where is the fuel set ie; plate or not and it's position? Where is the timing set?
Still could have some crappy full cuts or something that are hindering performance for your sized application. With a 3/4" wrench, DV socket and 20 seconds of your time you could provide more info.
Maybe it's a little low on compression. Some marine pistons are only 16.5 : 1, then if the builder went with an oversized gasket, compression could be in the 15:1 range.
Do you know what size washers were used on the injectors during install? The thicker stock washers, if used, might also be part of the problem.