Installing clutch pedal

[eric8]

I'm trying to put a clutch pedal on my 72 c10. I know the pedal shaft just slides onto the left end of the original pedal box assembly (in theory) but I'm finding I don't have room to move the pedal far enough to the left to get the pedal shaft in the hole! What am I doing wrong? Did you guys have to pull the whole pedal box to get the clearance needed to get the pedal mounted? Thanks!