You can't use the V of the 1.44" one, ALL of the mounting is on a different axis. I have two of those, and another short set. None of them looked to be suitable. You need to look at the stock coupler to see all the metal on every Lionel coupler is off-axis for the mount. Whatever you do, you're going to be fabricating the whole mount.
As far as the strength of the mount, I'm more worried about the Loctite 380 giving out than the fiberglass, that stuff isn't going anywhere! It's 1/8" plate, and I can put a piece of it between two bricks and stand on it! If it breaks, it'll be the adhesive, and I've had really good luck with the Loctite 380 for stuff like this.
