The entire dash assembly needs to be removed to gain access to the heater core. I would recomend purchasing a shop manual for that vehicle if you decide to do the job yourself.
What are the steps to change the heater core on a 1991Chevy S10 pickup ?
How do you change a heater core in 1994 chevy astro van?
6 quarts with filter
5.7 liter vortec.
Remove the dash, its located under the glove box. Becarefull it will puke out antifreeze!
how do you change the heater hoses on 1993 chey lumina 3.8 liter
Behind the glove box
It is possible but takes a while. Get a manual on your car from the parts store or DISCOUNTAUTOREPAIRMANUALS.COM