Your stein was made by Albert Jacob Thewalt circa 1960-1980. I couldn’t find the four liter version, but I did find the two liter version, mold 603 in The Beer Stein Library at https://www.beerstein.net/item.asp?ItemNum=the-0603. The Beer Stein Library has a Westerwald Handle Gallery. Select AJT and it will show some of the handles they made. I would suggest AJT 3, 4, 9, 11, 12, 16, or 42. I don’t know how much he is going to charge or what kind of work he will do, but you won’t be restoring it to its mint value. Take a look at what newer 4 L steins are going for. They go for about 1/2 that value in the after market.