msturg
+1y
That's not the way most people do a stockfloor, so your Z question is sort of out of the norm. If you did it the way you are talking, I'm guessing you would more than likely need to take 3" out of the bottom of the frame and then Z it. You prolly won't have to drop your motor but it might help for the extra clearance.
One question though, if you are going to go thru all the trouble of pulling your cab and such, why not do a more reliable stock floor? By using 2x3x1/4" all the way back from the factory clip?