If you wish to turn parts between centers with the headstock riser in place, you will also need to raise the tailstock the same amount. The P/N 1292 tailstock riser block was developed for this purpose.
NOTE: While parts up to 6" in diameter can be turned with the spacer block kit in place, it should be remembered that the horsepower of the lathe has not been increased a corresponding amount. Spacer blocks are intended for easy-to-machine materials or for an occasional job requiring more clearance. If the work you intend to do is consistently of a size that requires spacer blocks, you might want to consider a larger lathe.