Some starter/engine combos "might" use the spacer, some don't. There were several "different" noses on those delco starters used, so therefore IH had to adapt as needed. Not every vehicle/engine needs one. When sourcing reman starters, there is no telling "which" nose might have been used with the core for reman. Sometimes you did not use a spacer originally, but the replacement starter might require one...very frustrating!
Since your motor is on the stand, mount the starter with the flex plate installed and look at the starter nose "clearance" with the starter drive retracted, then manually extend the starter clutch and watch the actual gear engagement with the ring gear. It will be very obvious if a "spacer" is needed or not.
Also, is the motor an "original" to an s800 with autotrans? Are ya going back in with the borg warner slushbox or converting to a tf 727? The flex plates are somewhat different between the two and the ring gear position/spacing from the starter mount (machined boss) on the engine casting is a bit different also....same for the spacer between the crank hub and the flex plate.
