I would proceed as if I was going to renew the extension then you can't go wrong. I've never been asked for bank statements at 90 day reporting but they could. Report on line and it won't matter.
My advice would be to use an agent (if you need to) who takes you to Immigration Office and takes you through the process. That way you know what you are getting and where it came from and it is less likely that things will go wrong then or in the future. I insisted on paying half up front and half on completion which should not be a problem for a legit agency. It is quite possible then to get your affairs sorted out and obtain your future extensions yourself at your local immigration office. That is the course I followed and it worked out well.
If a branch turns you down this week go back next week. It can depend on who you see. I tried the same branch of Bangkok Bank 4 times before they said yes!
Sounds like you know the current owner and the vehicle is already registered in your home province. Next step is to ask at your local LTO what documentation they require to transfer your name to blue book. My LTO obtain a certificate of residence from IO for me.