Flaming River FR1506M Question

I just recieved my flaming river coupler FR1506M...for manual colume to manual steering box

My question is, the instructions say cut 1 1/2 inches off the end of the steering colume shaft. I thought I read on here "A thread on this forum" that an 1 1/2 is to much and only cut 3/4 of in inch instead.

Can anybody comfirm??? They look pretty easy to install...
I have been doing searches for the last couple of days and not finding much.

thanks Jim