Nice! I love some pewter. I don't know any other casters around here, but there must be some, 'cause there ain't never no pewter in the Thrift stores, and I check often.
Well there are a couple of options available to you, one you can do it like Beagle suggest above there. Another one is you can pick out one of your molds which might pour one up in the 220-225gr range with the tin and use them as 1/2oz pieces or if they drop out at about 110grs as 1/4oz.
Or you could do like I do with mine, I use the calculator posted up by Bumpo628 from here, Lead Alloy Calculators
I use a freeware program called Convert for Windows to convert it from ounces to decimal percentages of a pound. Then I blend it up into the alloy in a separate small pot and make up 1# ingots with it that way. I keep them in a small plastic box with the alloy name written on the top with a sharpie. When I use it up or change the sharpie wipes right off with a little alcohol.