Dean, not sure where you are seeing just the driver's side mounts advertised. For quick convenience, I cked Butlers website, and am seeing pairs, even though the Mity Mount is refered to as a mount. From longtime hands on experience with Pontiac, Olds, BBC's, and even 429-460 Fords, the torquing over of the V8 engine typically stress the drivers side mount the most. Pontiac, at least, was wise enough to use throttle cables on its '64 and later V8 A-body's & '68+ V8 Firebirds this eliminated binding of throttle rods/linkage, Chevrolet learned that one the hard way. In the early to mid 70's, Chevrolet had a service campaign to install small cable and bracket sets as limiters off drivers side motor mount to the upoer control arm shaft, this was on all mid 60's to '68 model small block cars and light trucks. This was a fairly expensive recall campaign due to the massive amt of vehicles built, and each different chassis took a different small kit. https://www.autosafety.org/chevrolet-motor-mounts/
Through the '80's and into the mid 90's I continually ran across these small bracket and cable packages in dealership buyouts. Many longtime Pontiac'ers have fabricated similar torque limiting devices using a fabricated pair of brackets & a cable. Others have fitted torque limiting straps or crude chains.
When it comes to replacement motor mounts, I stand by my earlier assessment, been ordering in, as well as picking up locally, and installing replacement older usage motor mounts for a long long time. upon ordering many, it seems to be only one mfg of our old Pontiac's rubber and steel standard motor mounts. Doesn't matter where one orders them from, the cheaply mfg mounts are the same. Jim's quoting OPGI's mounts as "built to stock specifications", well, i would have to put that as comical. All OPGI is doing is offering for sale the same thinner steel junk motor mounts, & since the holes line up, they can claim what they want to claim.
In respect to NORS (new old replacement stock) motor mounts, quite a few of us have sought them out & used them for years. Of the two dozen plus pairs I've installed/or sold to locals which have installed them theirselves, these what amount to 15 year old, to mid 70's manufactured rubber & steel mounts have proven to have held up very well. Much of that I attribute to how the mounts were stored. In the case of the large boxes of the Green Light stock I hauled in near 20 years ago, they had been indoors on the bottom shelves of family owned business. The large main room where the gondola shelving took up a good portion, had been air conditioned for decades. In such a favorable storage conditions, the rubber mounts showed no deterioration. Nothing like if they had been stored in hot shed with barn tin for a roof.
The replacement rubber & steel motor mount situation has slowly gotten worse as NORS supply's have been depleted. Down to two pair of "long style" Pontiac motor mounts that i personally need. Am also in a situation where need several more pair for upcoming projects. The whole mess is just something several of us have noted for several years. A long time specialty repair shop owner in the MetroPlex who happens to own numerous performance Pontiacs noted a few years ago on PY that in a period of over 18 months he'd had to put 3 pairs of replacement motor mounts in a customer's 74 SD T/A. All due to lack of a quality rubber & steel replacement motor mount. The '70-74 V8 Birds use the same long style motor mount, as do '70-73 factory 455 A-body's & '71-74 Pontiac B series. Its been very disconcerting situation, but I can report a solution is being prepared and it won't be a manfactured in India thin steel and rubber mount, or a version of that same junk import mount with a limiter bolt installed.