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The motor mounts are the same left and right, not different. The frame stands are different left to right, but not the mounts themselves.
You will, however, have to be careful which mounts you get. The low performance models (327/210, 307 in 69, and some 327/275 cars) got one type of mount, and the high performance (302, 350, and 396) got a different mount. If you get them from a local parts place, you may want to check the different engine sizes to see if replacements carry different part numbers for different sizes.
The original style low perf mounts had some issues because they were not interlocking, and the rubber could shear and cause the engine to rock, sticking the throttle open or other bad things. There was a recall that fitted a strap to deal with the problem. It may be that all replacements are now interlocking, but I'm not certain. You'll be able to tell by looking.
Either type of mounts will work for you, but the 302/350/396 mounts supposedly set the motor back toward the firewall a little. No big deal, but you might have to loosen the trans mount to slide it all back a little.
If you ever think you want to try to shoehorn a big GM style HEI distributor in there, the lower performance mounts are supposed to make that easier (as far as clearing the firewall).
You can get good quality mounts from someplace like GroundUp ( www.ss396.com
) or Rick's (www.firstgen.com)
, or like I said you can get them local.