Elsevier's article class for submission vs. the published version
It is very rare (in mathematics) that a journal really makes using their style necessary for submission, even for the journal making that claim in their guide to authors. My advice is to never adjust the style of a paper for submission, and simply submit the version you originally produced.
The reason is that formatting for each submission turns out to be a waste of time, all the more so that journal styles are rarely that much more readable for the referee than any standard style. (Note that unless you really know about typesetting you should not depart from standard style too much, e.g. do not use the fullpage package. Large margins have a purpose.)

In fact, most of the time this is not even mandatory to use the journal's style after acceptance, because the journal will do the job of adapting the article to their class. I try to do it for reasonably cheap journals (e.g. MSP journals), but I never do that for Springer and Elsevier.

Also, unless strictly mandatory (e.g. page limit) you should never change the content of an article in function of the formatting style (of course you can resolve overfulls and other warnings): the content is driven by what you have to say, period.