That's not rear intake as in rear disk, drum or bell intake, for better breathing and performance and whatnot. That's a piston-timed intake that happens to be in the back of the engine -- for low cost and to heck with the performance. It's probably the most modern-looking piston-timed engine I've seen (with the exception of the weed whacker engines) -- but I'm not much of a vintage engine mavin.
Piston timed engines are, uh, economical. No holes to be drilled in the crankshaft, no extra sweat over the crank to case seal due to the timing, no rear disks, etc.. And, they'll run just as badly well in reverse as forward!
I wouldn't be so cruel as to characterize it as a "fishing weight", but if I got one it would be for an old sport free-flight design that would be built for slow RC for sunny calm days.