I have 1 basically brand new Delta model# 14-651 mortiser here for sale. We have NEVER used this mortiser since we picked it up for my uncles house 10 years ago after his death! I assume that the longer drill chuck goes into the upper drill chuck, but I can't say for sure being we have never tried it?
The mortiser is just dusty from sitting in my fathers workshop for 10+ years, and it still runs fine once plugged in.
I also have 6 total, but different only 4 different size mortise drill bits. All the bits are basically brand new!