Hydro Junkie is correct. The wing rib profile is shown on the fuselage side view. Be sure to cut the ribs to match the outline inside of the outer wing sheeting and rib cap strips. Lacking the instruction manual, you might take a look at the build log below. It has lots of good photos and is almost as good as the manual.
Sig Kadet MkII build
Another way to make the tip rib outline is to get some poster paper and trace the plan outline of the tip. Then cut a strip of paper about 1.5 tines the thickness of the wing and as long as the wing cord. Wrap the tip plan along the top of the wing rib and then place the long rectangular strip against the bottom of the rib and lift it up to touch the tip pattern. Then trace the intersection of the tip plan against the inclined rectangle. The tracing on the rectangle should be close to the tip rib shape. Cut it out and play "paper-dolls" with it until you get the right fit. Now you have the tip template.

As for a replacement for the Thrustmaster 550 motor, I am not familiar with it. I know it was a series wound motor intended for nicad batteries and it would be hard to get hardware for it. Assuming your PT-electric is the one with a 56 inch wingspan and will weigh about 3 pounds with batteries, then I can tell you that you will need a motor of approximately 240 to 275 watts that runs on a 3-S 2200 mah capacity lipo battery and a 30 amp ESC. A trainer can generally fly nicely on a motor that can provide 80 to 90 watts of power per pound of aircraft weight, or produce thrust equal to about 2/3 to 3/4 of the airplane weight. A three pound trainer airplane would need about 900 to 1000 grams of thrust. You can usually find amperage, wattage, voltage, KV and propeller data for motors by Suppo, SunnySky and Leopard if you visit the websites for Altitude Hobbies (Leopard and Suppo) or SunnySky.com or Buddy RC for SunnySky motors. Based on this and assuming you can fit a 9" diameter propeller on your airplane, then a possible combination could be a SunnySky 2216 with a KV rating of 1400 rpm per volt, which (per SunnySky's data sheet) should turn an APC 9x4.7 prop on a 3S-2200mah battery sufficient to produce about 1220 grams of thrust and about 273 watts at 24.6 amps. A 30 or 40 amp ESC should do fine. This combo should provide about 8 minutes of safe flying time at half throttle and perhaps 10 minutes if flown at lower throttle settings.