The 1.9 was rated at 102 hp (gross), and 90 PS (about 88 hp SAE net ). Depending on who you ask or what magazine tested the car, 0-60 took anywhere from 10.5 to 12 seconds, and the 1/4 mile in around 17.5 seconds. Top speeds are debatable by many, but the majority of the magazines of the day all seemed to agree upon 115-120 mph top speed for a 69-70 GT. Vehicle weight is around 2100 lbs. Handling was not the car's strong point, most SUV's of today can pull more lateral G's than an Opel GT in stock form.
The good news is, all of these things are changeable and can be improved upon if you have the $$$ and the know-how.
You came to the right place....