for race use most definitely a good plan, road use, not so much, they transmit a huge amount of vibration through the cabin and make for a very rough, noisy car, mine were built out of some standard mounts which had split and failed, I removed all the rubber that was left from the lower half of the mount, and epoxied in a hockey puck, then I took the top half and drilled through slightly smaller than the thread used to hold the mount to the car, and dropped in a bolt, then another hole was drilled through the centre of the puck and the flat plate at the bottom of the mount - put in some wide flat washers either side of the puck to spread the load. Finally it was bolted to itself and the car. Because I was flat broke it kept the car on the road with minimal damage to anything else, but I wouldn't and didn't want to keep it for a day longer than absolutely needed. Back to factory hydraulic mounts and we are back in church mouse territory. Much better.
For racing, I can see no reason why not, its simple enough to fabricate something from stock parts and by the look of it I reckon fabricating a bespoke piece would be easy as well, however for comfort, I would probably add a sliver of rubber somewhere in the build to take out a little of the harshness.