First, welcome to MO. You will like it here and you will get answers to any question or problem. It's nice that you now have your Granddaddy's 336 as he wanted. I'm sure you will treasure it.
If it has a walnut stock, pistol grip with a white line spacer and a full length mag tube it should be a 336C. If it has a straight stock (no pistol grip) it is a Texan.
A photo will help us to identify the 336.