Hi Guys,How hard is it to replace a timing chain on a 1994 Ford F 350 with a 460 motor ?

 

In comparison to what?
"How hard" doesn't tell me anything about your abilities/experience, tools and work space.

Consider... you have to remove the radiator, entire front dress, harmonic balancer, water pump, timing case and anything else in the way.

Typically on a vehicle this old there is a lot of scraping and cleaning of parts and gasket surfaces.
You may want to go back with a new water pump and backing plate.
You may need to sleeve the balancer or install a new one so the FMS has a clean surface to ride on
Good time to install a fresh belt and tensioner.

You'll definitely want to thoroughly clean the engine before opening it up.
Be careful when scraping the front of the block that you don't drop a bunch of stuff in the oil pan.