Great Guns

With the Great Guns routine that I am trying, for the first phase one of the exercises is the bar curl on the preacher bench. However, my gym only has a preacher curl machine, and it is setup in a way which makes it impossible to do curls over it holding a free weight barbell or ez-curl bar. So my question is, is it better to replace the curls with normal standing bicep curls or just do it on the preacher curl machine?

Either one is an acceptable substitute. I would lean towards using the preacher curl machine because there is already some regular standing bicep curls in that phase. Take advantage of the unique position of the preacher curl even though it is a machine.