If you have or can get some 318 mounts, you can just modify them.
Top pic is a proper 340 mount, second is a factory 318 mount, third is 318 with addition of a screwed on extension plate, and fourth is 318 with welded extension.
Last pic is a before and after of a 318, mount cut narrowed welded, and leg added version.
Pics are compliments of other FABO members, I found in other threads.
But if you don’t want to get into fabrication, then a want add is going to be your remaining route.
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