You may be able to do this working with the source files... but it can be tricky. Make backups of your forms first.
My thought would be, if the data sources of the two forms is exactly the same, I'd pick one form and add a new view to it. Then I'd save both forms as source files. I'd copy the contents of the original form's default view file (probably view1.xsl) into the new view xsl I just created. Might be worth a quick try, but I've never done it, so I have no idea if this would work...