Toyota 4Runners used the same basic engines from 1990 to 1995 (22RE 4 cylinder and 3VZE 6 cylinder). Swapping an engine from a 91 into a 93 should work fine if they both had the same engine type to begin with. To be extra safe you should make sure to transfer the ECM (Engine Control Module) from the 1993 along with the engine and associated wiring. Of course this is not a simple job. You have to think of all the things bolted to the engine as well, like power steering pump, AC pump, alternator, anti-pollution equipment etc. The YotaTech 4Runner website (https://www.yotatech.com/forums/f116/) is a great resource and members of this site have done this swap.