Main Motorcycle: 06 Thruxton
Join Date: Aug 2008
Location: Winter Park, FL USA
Other Motorcycle: '69 Bonneville
Extra Motorcycle: '71 Bonneville
I am not familiar with the lever you have on your backing plate. My guess is that it is something fitted by who ever modified the bike and bent to fit. But, I don't know for sure that it is not a stock piece from some year Triumph.
The lever on the backing plate of my '69 looks like Moto6T's '64-66' example, a flat lever.
If you want to use the new plate that you show in your first post and the new levers that you mention that you obtained, you will need to find a flat backing plate lever to align with the "inside" lever.
If you have the engine plate that works with your "outside" brake pedal shown in your second post why not continue using it?
Something that I did notice about the "new" plate shown in your first post with the welded boss, it does not seem to have the third bolt hole for the stock frame tube that heads up to the shock mount. It appears to be cut off and the plate rounded on the rear side. Or is this a home made plate?
At any rate, the hole in that plate (in your first post) that is above and forward of the boss for the brake pedal would normally be the hole for the swing arm attachment, something you would not use if this is a hard tail. With out the need for a swing arm mount and no mount to a frame rail for the third bolt I guess the only job for this plate is to support the brake pedal. It would remain to be seen if there will be sufficient support for the engine with out the rear mounting plates.
Good luck with your build, Art.