a border run and a subsequent visa-exempt entry, or a visa-run to Vientiane and the application for a 60-days Tourist Visa does not make any sense at this point. This is because of the recent "overstay", he CANNOT use the "change of visa type" from a TR visa or a visa-exempt, to a 90-days Non-Imm-O marriage visa anymore. Your ONLY chance is either the "Multi Entry 365-days Non-Imm-O family visa" (or the "90 days single entry Non-Imm-O marriage visa") from Savannakhet, OR he flies back to the U.S.A. and applies for the Non-Imm-O marriage visa over there. The Savannakhet option is absolutely doable, a few hundred of expats do this every year and the officials at this consulate are super friendly.
Pong Nam Ron is the Myanmar border, which is closed for foreigners by now. I would emphatize that your husband flies or drives to Mukdahan, and from there to Savannakhet, Laos (as Vientiane asks for appointment and for the financial proof!) You should accompany him (although your presence is not actually needed, yet is better for the overall picture and you will have to sign documents when there). You need your fresh Thai marriage certificate, your blue housebook and Thai ID-card, and a few other documents (that are listed on the Thai Consulate Savannakhet website under the "single entry 90 days Non-imm-O "family" visa") The consulate offers a walk-in service. Your husband can apply for the "365-days multi entry Non-Imm-O family visa" based on being married to a Thai wife. The fee is 5000.- Baht. Savannakhet is the ONLY one of two consulates in the region (the other one being the Thai consulate Ho Chi Minh City) , where your husband can receive the "1-year Non-O marriage Visa" WITHOUT any financial proof! Upon each entry within the one-year visa validity period, into Thailand, your husband will get stamped in for 90 days stay permit. The 1-year visa will give you plenty of time to amass 400,000.- THB on a Thai bank account in his sole name. He will need this financial proof to be able apply for the "1-year extension of stay permit based on marriage to a Thai wife" (which some of you call "marriage visa" yet actually is not a visa but a stay permit)
collect all the documents you need from the university, get your Vietnamese marriage certificate, collect signed by him copies of his passport, the visa page, and all other documents, copies signed by him in blue ink (!), and fly to either Hanoi or Ho Chi Minh City. There at the Thai embassy/consulate, you can apply for the "trailing spouse visa" as a dependent of your husband
sorry to say, but the Thai embassy and the consulates in the USA discontinued handing out multi entry Non-Imm-O retirement visa. Only single entry can be had, and the 1-year multi entry Non-Imm-O/A visa
just wait until your next extension is due. It seems they want proof of your income source, so they can tax any earnings you transfer to Thailand, by next year. since many countries have a "double taxation agreement" with Thailand, the source is important for the Thai tax authority. So they will not just accept a WISE transfer but actually need to know the source . . . it seems to be the road to the OECD "world income" taxation
I got the DEEP suspicion that this is just the beginning. Thai government plans to put a tax on foreign earnings coming into Thailand. So this would explain why they are beginning to collect proof of pension income from now on, which they can pass over to the tax authority by next year