I just ordered a new caliper for my 71 GT from Opel GT Source since my old one was leaking and needed to be rebuilt. I believe it was about $99 before tax, shipping and an additional $30 core charge. I was VERY please with the excellent quality of the rebuilt part!
If you read the OPEL GT GOLD PORTFOLIO most of the auto magazine reviews rate the brakes as "good". I would agree good to adequate. Opel GT Source has a Front Big Brake Package (item #4003SP) that you can order to increase your front braking for $699 plus tax & shipping. They also have "FRONT IRMSCHER VENTILATED BIG BRAKE PACKAGE Includes special hubs and rotors, 1975 calipers, and a kit to widen 1975 calipers. Improved braking for racing applications. Best Opel GT front brake package money can buy.," OGTS for $1,100 plus tax and shipping.
Of course why stop there??? LOL they also carry rear sets you can order as well. Visit
Opel GT Source --- Welcome.
You may also want to call and talk to JIM at USA Opel/ Opels Forever at
USA OPEL .
It all depends on if you want to restore, upgrade, or build a sports machine and how deep your pocket book goes.
Neil