SkipM,
Generally speaking with my Super Shrews over the years I go with 10-15# over marked weight at 28" draw (29" arrow) and 125 grain point.
Example, I'm shooting tapered Surewood shaft in 60-65 spine range with my 47@29" Super Shrew drawn to 29 inches with a 30" BOP arrow and 125 grain point(44@28+3#extra draw+5# for 1" extra arrow+10# low end of 10-15# extra for bow/string type)=62#.
You've got 35 grains more (approximate 1# of bow weight for each 5 grains), so roughly 7# of spine extra for your heavy points.
So to get you in the ball park for your 50# Shrew, I'd start with 50# plus 7# for extra point weight and then add 5# for 1" extra length on arrow and then 10-15# for style of bow/string. This would put you into a 70-75 arrow spine.
Now that I've said that, I'd order a test pack of shafts (I like the Surewoods) and you can get them from Wilderness Arrows or Braveheart and really make sure you're getting dialed in for your bows. Since you're trying to match 3 bows, this might be the best route for you. I'd suggest getting a 4 spine pack starting at 65-70 and going to 80-85 OR 60-65 and going to 75-80. This gives you 3 arrows in each spine group to see what groups best for each bow.
You can also double check with Ron LaClair too. I believe he used to recommend 15# over marked weight for spine. He also sells arrows made by Paul Jalon and I shot some up at Shrewhaven this fall and they flew great and of course are beautiful.
I'm sure any of them can get you fixed up with an GPP arrow weight that will work for you.