Great analysis CGiD! If I was in the OP's situation, I would be asking you for advice. It is a difficult decision to make if the OP plans to apply for a mortgage in the next couple of months. The OP is right at the borderline. A mid-score of 739 vs a mid-score of 740 is huge.
Let me add one more thing to consider. Moving often entails HP's. Whether it is applying for a lease or utilities for your house before you close. Shopping for mortgage rates will also involve multiple hard pulls (which should be combined into one HP for scoring). The score pulled for the final mortgage pull may be a few points lower now.
I think I am with CGiD, the safest course of action would be get the SSL and wait for your AAoA to hit 2 years before applying for a mortgage. Perhaps a good middle ground would be to join Alliant and add $550 dollars to the savings account. You will be ready to app for the SSL if needed. Once you are sure the closed installment loan has reported to EX, pull your EX mortgage score again. If the score has dropped below 741 (or whatever) proceed with getting the SSL. If you do not need the SSL for your EX-98 score, Alliant has good savings rates. It makes a good place to stash your down payment while shopping for a new home. Or even get the mortgage through Alliant. Alliant does more than SSL's.
My last piece of advice is if you like to monitor your mortgage scores long term, look into some of the free ways to get your mortgage scores. For example, NASA FCU provides free monthly EX-98 scores. Plus they would be another CU to check mortgage rates (note: I dont' know which states they write mortgages for). DCU (and several smaller CU's) provide EQ-04 scores. However, I wouldn't join DCU right now as they HP your EQ to join. NASA FCU does NOT HP for joining.