Hi Mick, the front clevis modification (extra two bolts) is definitely something to consider. The F-9's hardly had any problems on Series 3's unless the plane went up on the nose ect.. It woud be a judgment call on you to either go with thicker metal or go back with original.
There are quite a few minor mods that can be made in certain areas. George's plane incorporated many (if not all) the improvements below. You guys can help me out with any I miss or others you feel are good.
Compression tube motor mounts with improved motor mount pads
R-3 rib doubler
Capstrips (We have always stripped top and bottom all ribs)
Box section stiffeners
R-8 doublers
Sharp trailing edge
Improved throttle cables (and engine attach brackets)
Throttle quadrant rear cover
B-7 bushing doubler
G-25 (end of the wing plates) strengtheners
If you have looked at pictures of George's plane you will notice he also has a different type bucket seat, self retracting (reel type) shoulder harness, and upright mounted fuel tank.
One question I had was what caused your engine failure ? Some common reasons for failure include carb coming loose, sparkplug cap popping off, or compression release failing.