How do I modify cooking methods for a markedly smaller roast than most recipes state?
It is past Easter but for future you may want to try this.  Get a saute pan or a saute pot you want to roast in, heat it and then brown your roast, all sides.  Before you do that, be sure you season your roast very well so that when you put it in the hot saute pan with the oil you are browning the dry seasonings also (be generous with your seasonings).  Once well browned take out of pan or if large enough pan take out of pan, put a rack on the bottom of the pot put the roast back in, cover, put in preheated 350 degree F oven for about 45 minutes to l hour, covered.  Temperature of roast should be 145 degrees for medium to medium rare.  Let sit for about 20-30 minutes.