An easy way to make the 3/4" cut is to set up your carriage stop where you want to stop the cut. Use a 3/4" spacer between the stop and the carriage to position the carriage and insert the new stock so a light facing cut can be taken. Remove the spacer and turn to the stop for your 3/4" length. As far as the diameter goes, I usually just rely on my DRO reading. Sans DRO, the cross feed dial can be used.
For a second op on a partially finished parts, I will use a spindle stop. Here is my version.
I have used a part stop in my old Craftsman lathe headstock for many years. When making multiple parts, it provided accurate positioning of the parts in the chuck and it allowed removal of parts for measurement when machining to precise lengths. When I bought my Grizzly G0602, I really missed...
www.hobby-machinist.com
If using 5C collets with a collet stop, caution should be used. Variation in tightening the collet will result in inconsistent placement of the part with respect to the carriage. A spindle stop would be preferred for accurate replication.