Originally Posted by From the FAQ

Will a 3rd Gen RX-7 (FD) twin turbo engine (13B-REW) fit in my 2nd gen RX-7?
The simple answer is No! The motor mounts are in different locations as well as other issues; however if you have enough time and money it can be done. Much of the project will be custom fabricating all the systems that attach to the engine such as the exhaust, intercooler setup, cooling system and wiring. A standalone EMS is almost required and it is very difficult to control the sequential turbos. Most people go to a single turbo because of this. In general this swap is not worth the time and trouble unless you plan on making more then 450 HP.

Here is a basic write up: http://fc3spro.com/TECH/SWAP/FD3S/rew.html

There have been many past threads covering swapping the 13B-REW into an FC:
https://www.rx7club.com/forum/showthread.php?t=724758
https://www.rx7club.com/forum/showthread.php?t=721243
https://www.rx7club.com/forum/showthread.php?t=717051
https://www.rx7club.com/forum/showthread.php?t=718967
https://www.rx7club.com/forum/showthread.php?t=636334
https://www.rx7club.com/forum/showthread.php?t=713592
https://www.rx7club.com/forum/showthread.php?t=712829
https://www.rx7club.com/forum/showthread.php?t=710959
https://www.rx7club.com/forum/showthread.php?t=710360
https://www.rx7club.com/forum/showthread.php?t=699306
https://www.rx7club.com/forum/showthread.php?t=690691
https://www.rx7club.com/forum/showthread.php?t=686057
https://www.rx7club.com/forum/showthread.php?t=628090
https://www.rx7club.com/forum/showthread.php?t=681876
https://www.rx7club.com/forum/showthread.php?t=663582
https://www.rx7club.com/forum/showthread.php?t=674513
https://www.rx7club.com/forum/showthread.php?t=672656
https://www.rx7club.com/forum/showthread.php?t=668437