These had an optional 8hp Briggs, so theoretically the 7hp (if flathead) should be able to fit w/o the nice cutout in the rear body. By far, most came with the JLO L230. I've never seen an original 4-stroke version in person, but I do have a few photos from original brochure for the 4-stroke. Not sure what all is different on 4-stroke except engine frame and clutch. You have your work cut out for you so good luck.
There were at least a couple of good dealers for these in TX, so there should be a few still scattered around. My buddy got a beauty out of Waco 3-4 years ago. Original survivor... 30+ years in indoor storage.