The following is from the USCIS website:
Under provisions of immigration law, to qualify for returning resident status, you will need to prove to the Consular Officer that you:
Had the status of a lawful permanent resident at the time of departure from the U.S.;
Departed from the U.S. with the intention of returning and have not abandoned this intention; and
Are returning to the U.S. from a temporary visit abroad and, if the stay abroad was protracted, this was caused by reasons beyond your control and for which you were not responsible.
I do not believe he qualifies for an SB-1.
There are many ways for him to become an LPR through you. K-1 is one option; if you want to marry him in England, K-3 and immigrant visa is another option. If he's here, he may be eligible for adjustment of status.
You should sit down with an immigration attorney to discuss all of the options.
What are the chances he'll be able to do so with an SB-1 visa?
Zero. " he just had a visit and turned his LPR into customs at the airport."
Or would we be better off going with a K-1 or some other option?
If the intent is to get married, K-1 is the only option.
You should retain an experienced immigration lawyer, whether myself or one of my colleagues, to review all the facts, advise you, and handle the case.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.