This is the style I used for my 351 to 429 swap back in '86. Just looked at the engine out in the garage and it's got the steel block-to-isolator brackets, and then the same isolator shown in your link.The isolators for the O.E. 1971 Mustang only 429/460 engine mounts (the style that have a bracket that bolts to the engine with two studs, then the isolator and unique 429/460 frame stands) are available from Don @ OMS:
https://www.ohiomustang.com/store/order_page.asp?itemid=2559
These isolators are common with 67-70 Mustang/ Cougar FE engine isolators. Sometimes searching for this application not 71 Mustang/ Cougar 429 yeilds better results.