Engine mounts are the same, the only real difference that I know of is that the 360 uses a different oil pan, and the harmonic balancer, flywheel/flex plate are unique to the 360 as well.
Yes, you will need one that has the correct external balance weight for the 360. Also, you may need to check that the balance on the torque converter is correct, but others may want to chime in on that.
Mancini racing sells a special right side motor mount. It's tougher than a stock one outta a auto store. I'd recommend that or with those kinda ponies your pushing a normal mount will last a year.
I would have the engine neutral balanced so you could run the 340 flex plate and harmonic balancer. That is what I did when I built my 408 from a 5.9/360.
I looked up your engine on Chris's site, and it is external balanced. Have him put on the flex plate as part of the deal, and then go with a zero/ neutral balanced converter.
Go here —-> '70-74 E-Body Products
And then scroll down for (hopefully in stock) better engine mounts and/or a engine torque strap that holds the engine in place incase of motor mount failure.
Engine swap step one; Find out how the engine was balanced.
If it is balanced externally/stock, then a B&M flexplate can be purchased that solves this issue. There also sfi rated.
If internally balanced, make sure you have the proper balanced up front and a zero balanced converter.