The first question to ask is, what kind of alignment would you like to achieve. Baerwald? Loefgren? Rega?
Most people prefer the Baerwald two-point alignment, which produces the lowest distortion across the whole side. Unfortunately it may not be possible on a Rega arm. If your 900 is mounted at the standard Rega pivot-spindle distance (222mm) then the cartridge will have to be very near (or perhaps beyond) the end of the slots to reach the Baerwald points. OTOH, if you can move the arm closer to the spindle (219.5-220mm works well) then a Shelter is long enough from stylus-to-mounting holes to make Baerwald alignment achievable.
For a poor man's version of a Wally Tractor for Baerwald alignment, go to www.turntablebasics.com. Their $20 printed protractor is not quite as accurate as an etched Wally, and it does require accurate aiming at the arm pivot. OTOH, it's mirrored like a Wally. This makes alignment of the cantilever MUCH easier and more accurate.
Most people prefer the Baerwald two-point alignment, which produces the lowest distortion across the whole side. Unfortunately it may not be possible on a Rega arm. If your 900 is mounted at the standard Rega pivot-spindle distance (222mm) then the cartridge will have to be very near (or perhaps beyond) the end of the slots to reach the Baerwald points. OTOH, if you can move the arm closer to the spindle (219.5-220mm works well) then a Shelter is long enough from stylus-to-mounting holes to make Baerwald alignment achievable.
For a poor man's version of a Wally Tractor for Baerwald alignment, go to www.turntablebasics.com. Their $20 printed protractor is not quite as accurate as an etched Wally, and it does require accurate aiming at the arm pivot. OTOH, it's mirrored like a Wally. This makes alignment of the cantilever MUCH easier and more accurate.