dont diet. i assume your wanting to gain weight and strengt in the long run... dieting will inhibit this.
you mentioned wanting to get to a certain ranking... my advice, dont worry about it! its an illusion. powerlifting is so watered down with different federations, its almost impossible for any ranking to really mean anything. hell, your lifts could win a "world championship" if you went to the right meet... but then again, you could compare yourself to the guys in texas high school powerlifting and find that you wouldnt even qualify to go to the state championsips.
just lift for yourself, try to improve, and be happy when you break your own personal records.