Its not much harder on an RX7 to do a manual swap than anything else. Unless the motors been well maintained it probably does need a new one. You can put a newer motor in it but the best bet for that chassis is to go with a Turbo II's motor and drivetrain. You can buy them as a set from MazMart and many other junkyards. The REW motor is great but will bring you many headaches for not a lot of gains.