Do you want 24 frets? Or do you just want a neck to use the s body? Because the 540s 540r and 540p from the 80's and early 90's had a rounded heal like a fender strat. If it is a fender style pocket you could get a custom neck made for it from warmoth or another manufacturer.
The attached image is one of my 540R's the neck is not an ibanez neck... I have another custom neck to be delivered here any day now... They are from bestguitarparts.com. If you don't mind not having an ibanez headstock... it's a great solution. I also have a js100 with a warmoth neck (essentially a 540r body). That's the black one. The warmoth neck just needed the frets polished a bit and the mounting holes drilled. It is maple, rosewood fingerboard, stainless frets and moon glow inlays for the fun of it.
The Best guitar parts necks need some finishing, but they are killer when they are done. The one that should be arriving soon is for my 91 540r LTD. I can't get past the shark tooth inlays of the stock neck... The ultra neck is nice and all, but I just can't deal with those inlays haha. The new neck has all the options you could want! Roasted maple shaft wood, rosewood fingerboard, graphite reenforced truss rod, 14" radius... And stainless frets! All for $360. I know some people love that ibanez headstock.