Some use 1 solid mount on drivers side only
https://www.summitracing.com/parts/mor-62520/year/1971/make/dodge/model/challenger
Description: These mounts are made for racing. Moroso solid steel motor mounts replace stock, OEM-style rubber mounts to prevent torque loss and binding linkages, a common result of excessive engine movement. These solid steel mounts eliminate the need for bulky torque straps and chains and are covered with a protective zinc coating.
I drilled a hole for 1/2” counter sunk bolt through stock mount. This picture is before I finished welding all around. Used nylock nut with 1/16-1/8” gap at top to allow for engine vibration. Drivers side only.
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I used energy suspension poly transmission mount, holding well on 4 speed 340 car. Rock auto has them also summit.
And you can do
Broken motor mounts.....here's the fix
Basically, what you'll be doing is drilling a few holes through the mount and rubber biscuit and installing grade 8 hardware. There are no torque straps or chains needed and the mount looks perfectly stock. I use a conical head bolt along with a flat washer and nylock nut to keep everything in place. The nylock will not back off or need to be retightened once it's installed. The idea is to just snug up the bolt so that there is:
(a) no compression on the rubber biscuit
(b) protection from separation due to engine torque