I AM A BACK YARD MECHANIC, IS CHANGING THE HEADGASKET SIMPLE TO DO ?
No. What kind of work have you done?
Not something I would do, and I’ve been working on my own cars for 50 years.
Cars like my 73 Vega or 68 Firebird…I wouldn’t hesitate replacing it myself.
But newer vehicles are a lot more complicated…lot more to take off just to get to the head gasket…And the room to work on some of these vehicles is almost non existent.
Yes, newer vehicles are more complicated, but…if the OP is located in The US, the newest that this Cressida could possibly be is a 1992 model. And, there is the possibility that his Cressida is even older than the '92 model year, which would translate into a much less complicated arrangement under the hood.
Then, when you factor in the reality of an I-6 driving the rear wheels, the engine compartment setup is about as straight-forward as you can get for a car of the '80s or '90s–i.e.–much easier access than later-model FWD vehicles.
The one unknown factor is the OP’s skill set, but if he obtains the factory service manual for the car, if he has the right tools, and if he proceeds with care, there is a decent chance that he can do it himself.