Oh ok bummer.
My situation was opposite,
My car came with a 340 but when I bought it someone had put a 318 in it and bent up the 340 mounts to fit the 318...lol
I probably still have them and most likely can be fixed.
I'll let you know if your interested.
Thanks but I did find some 318 ones on ebay, though it looks like my 273 ones can be modified to fit.
One way or another I'll get the brackets sorted out.