So this boat has the AIRE lace in floor? If so, just move the thwarts forward and backward until you know where you want to be. As R2, you might be moving the rear thwart forward (you might also have to move the forward thwart forward). In R2, I personally like to be slightly forward of center. For R4, I like the group weight to be slightly forward. R3 you will probably move everything back, while having you crew forward of center. R5 might be tough configuration and the boat will be heavy. Use a sharpie to mark the pvc at the floor lacing location as you figure them out. I used black dots for my normal positions and red or blue dots to signify where I move thwarts for various configurations. Once you have "normal" locations, you can use split links
to run the thwart strap through. I also use these to tie gear down in the boat. pulling and pushing the webbing straps through the floor lacing all the time will eventually abrade the floor lacing. I would not glue in foot placements until I was 110% positive.