Alpine951

I am doing my first belt and seal job on my car. The belts are all off and the front of the motor is sprocketless except for the cam. I found some posts here that some people thought that the collar holding the sprocket was 32mm. Clarks garage site says it mught be 1 1/4". From what I understand, I need to hold the collar still while trying to loosen the cheese head bolt in the end of the cam so that the valves don't bang up against the pistons. My car is an 86 951. I tried a pair of pliers around the collar with a piece of lead pipe on the end of a socket for the cheesehead bolt. That aint gonna work. If I had someone else holding the pliers and collar while i did the cheesehead it might work, but I am doing this by myself. I would like to know the actual size before I run out and buy the wrong size. Or if anyone has some insight as to what worked for them, thanks in advance.