Oh yes, Jeff, another case of clear sight but we don't see it. It's on casniffer's Classic Pattern pages
www.trentonrcflyers.com/pattern/articles-plans-instructions.htm (the Astro Hog article you'll find appended to the Smog Hog article).
Maybe you can still use some Simla details. It was not possible to measure the clipped wing from the pictures, but Cees' method of building a model and comparing the pictures works. I clipped the wing tips of the virtual Simla by 3.5" and left the tip shape alone. Now it seems quite clear that the wingtips were smaller and had not that "sweep" or "rake" like the original tips. Makes it more likely that the rib frames were 3" wide, one was cut and the new tip blocks were made smaller/narrower.
Side note:Still you may design the wings so that both ways of clipping are easily possible, as described above.
Question
o you think Ed shortened the fuselage?
As to the engines used: Electric is natural for Simla due to its low wing loading. Even a quite small AXI 4120 suffices and makes for the same aerobatic performance as the .61 glow engine. There's plenty of room in the cowl, just use a rear mount. Some cooling is advisable, for instance by a NACA duct intake on top of the cowl behind the spinner and an opening on bottom where the nose landing gear is.
The landing gear in original length is right for electric power with a 12x8 prop if dihedral is 2 degrees (instead of Ed's 4 degrees). Every 2 degrees dihedral make for 0.4" landing gear height. A .91 four stroke with a 14x6 prop should have 1" longer legs and a 1.30 four-stroke 2" longer legs for 1" ground clearance.
It's no problem to change the landing gear legs when changing engines, but the longer legs (at least the 2" longer) should be different if you're flying from grass. The same wire diameter is good for the short and long legs because the longer legs are just more springy and don't give too much load on the wing and firewall, but for shock loads on grass they might be too weak. Thicker wire requires strengthened structure and makes for more weight.The drag is not noticeably higher but its center is noticeably lower, giving a drag moment to balance. Bigger wheels have substantially more drag.
A big RCV 130-CD has no problem with this drag. In fact, it makes for more drag itself. It requires the firewall to be set 1.75" back, so the engine compartment is 5.75" long (or make it 6"). The firewall should be a bit wider and taller, but the fuselage nose looks more pointed and elegant.
The RCV 91-CD four-stroke is a drop-in replacement for a .61 two-stroke, as advertised. But you have to mount the manifold and carburetor outside the fuselage. Unfortunately, it can be turned only by 180 degrees so it sticks out even farther than the cylinder head, what looks weird and nasty. A 1" longer engine compartment is enough to accommodate the carb.