I changed my 326 motor mounts I just used 400 ones they fitted fine now I have taken the 326 out and put a 350 in using the same 400 motor mounts.
67 Firebird 350, TH350 auto Convertible, B&M 3000 TC, 4bbl Edelbrock Performer carb and intake Black Jack headers,disc brake conversion. 10 bolt chevy axle with 3.73's and B&M Rachet shifter.