The factory setup is two piece. There is the mount (Insulator) and an adapter plate to the block. I bought the set of all four pieces recently for about $230. If the frame adapters are 68-70 SB you have to drill a hole to change their angle to match the FE mounts. The 67 SB frame adapters are drilled the same as the BB.
The other option is the aftermarket style like the OP asked about. That is a two piece design that gets rid of all three factory pieces and give you a positive retention setup that will keep the mount together under high torque. The original setup has a mount that uses rubber bonded to metal and if it tears your engine can move freely. You can also adjust the engine mount location fore or aft about 1/4" or so which sometimes can help like with headers and a Borgesen steering box. The down side is they do not dampen vibration as well. I know some have gone back to the stock setup because they did not like the extra vibration. Guess is a personal preference there.
Regarding RockAuto 67-70 Mustang/Cougar engine mounts just looked on their site. Looked at 68 and 70 Mustang 390 and 428 listings and every mount was wrong. One was a 302 mount, another was for a T-bird, the other for a truck. Rockauto can be great, but you have to make sure the parts list are correct!