Check the drive system. If it's older it'll have two arms on a regular cam that is integrated into the head-lift. Newer models have a banana cam that is independent of the head-lift.
Either way, if there's some extra chunk on the arm/banana cam, you can drill and tap those, and then drill extra holes on the extender supports. You'll have to play with locations to see where the stroke will begin in regards to the frame edge. Will the machine even support a frame that can print 18x24?
It can be done, it is some work, probably not worth it for such a small machine. You'd be fighting it every time you want to print that big anyways. Keep your eyes out. I just picked up an M&M 25x38 for free.
I watched this SPE 4 poster 40X57" sell on Ebay for $2000. I don't know the brand, but damn that seemed to good to be true.....probably was.
Electric motor beautifulness, nice and CLEAN looking. Someone should have been all over that.
Personally, I'd be looking at something a little more useful than an old cameo. They're good for what they are, small footprint, reliable, etc. They're just small, and limited in adjustability. I consider them the broken rollerskate with clay wheels of screenprinting. Not to say they're total shit, but you can do better with a better machine, with a little more money.