Since prints are developed to near completion, the paper pretty well determines both the contrast and the image tone. The developer has some effect, but not a whole lot. You might look into Agfa 108, Beers No. 7, and the high contrast mix of D-64 to get a little more contrast. Amidol also gives high contrast, but it may warm the image some, and it always works fast. Diluting the developer lengthens the working time, but it may warm the image a bit with some developers. I've used Dektol at 1+5 to get some more time, and I've seen recommendations for dilutions up to 1+14 for some similar developers.