Is a transition & reclass to Reserves possible?

Once you're within six months from ETS you can sign a contract with the USAR or USANG. If the position you sign for is a "will train" slot then you can retrain into that MOS. It may be a year or two before you go to school since you are already MOS qualified. There is almost no AIT you would PCS to unless you are attending the SF Q Course. The RC also has some AIT classes that are broken up into two week portions. It's very flexible so that you can work it around your schedule.
You will keep the rank you make and if you are still promotable when you transition you will keep your promotable status.

Prior to your ETS you seat down wit a Reserve Counselor, National Guard equivalent, or both. They will give all of the answers you seek. Regarding of rank, there’s no demotion. You transition with whatever rank you have. By the way, you don’t need to wait for your ETS to go and chat whith them. The sooner you do the more information you’ll get!

Edit:

Also, you don't PCS. You are authorized (to include family members) travel to your Home of Records or whatever place of your choice (more than that but not going to cover it).

When it comes to transitioning from Reserves to AD, your options would be limited to what's available according to the most recent Prior Service Business Rules. The most current list and rules went into effect 19 February 2019. The rules indicate that a "reduction in pay grade will not be considered, no exceptions." As far as vacancies by grade and MOS, there are no 68 series open in the grade of E-5. For E-6, 68W is available (with current licenses/certifications). Options for re-class in the grade of E-5 include 10 MOSs, but not of them are 68 series. There are not current openings to re-class in the grade of E-6.