Go to seadoomanuals.net and get the shop manual for the 94's.
The 147 degree valve is correct for the gtx. The 159 degree is used in the 657X motor which was used in the XP only. There are two 657 motors in seadoo history. The 657x was 5 more HP more than the 657 and relied on a different rotary valve, rotary valve cover, carbs, pipe, cylinders and maybe some other things.
Personal observation, since I own both a gtx and xp 94 models, is that seadoo wasted a bunch of time building the 657x since it really wasn't that much more over the regular 657. The 657x showed up in 94, was used in 95 and pretty much abandoned after that. Even when I was setting these machines up out of the crate we in the shop talked of switching a gtx motor into the xp hull since the gtx ran so much smoother, had a holeshot that made the xp look stupid and was only a few mph slower. Even the ski-doo test and tune crew we worked with commented on how bombardier liked their "experiments" that got put into production, cost too much to develop and tool up for only to have them last a few seasons (657x motor, skidoo stratos/escapade - 90's era safari series - 2000 era single A-arm front fan cooled sleds, mach z 1000 twin, formula plus efi.).
A cure for the 657x xp, I found, is to raise the pop off pressure to the mid to upper 20's, take out the stock impeller that was pitched too high and put in the RH impeller from a speedster with a 15/20.5 pitch and enjoy. A simple fix that makes so much difference. The gtx still edges it in a drag race off the line.