I agree. Unless my memory is totally failing me, 273 and 318 block mounting ears are the same, and a bracket for one will exactly fit the other. Likewise, 340 and 360 are the same, and a 273 or 318 bracket will need to be slightly modified to fit the 340/360 block ears. So - if you already have the 273 mount brackets, use them.
On the driver's side, four washers on the rear bolt will be sufficient to adapt the 273 mount to a 340 or 360 block.
On the passenger side, weld a triangle on the side of the 273 bracket that has one bolt hole, to match the other side, then drill one hole. Presto: a 340/360 mount bracket.
Here's my 65 Barracuda driver's side 273 mount bracket bolted to a 340 block. The 65 273 bracket is different than 67-later 273/318 brackets, but the width is the same, and how you make it fit a 340/360 block is the same.
View attachment 1715476080