the heater core in question is the Chevy Chevette heater core; any year from '76 to '84 will do; they are all the same. if you dont have the tools needed to mod them however (the standard inlet is 3/4 inch, and the outlet is 5/8 inch. you'll have to cut those fittings off, and solder new ones on), it would probably be better to just get the DDen heater core.
as for the pump, you can save yourself some cash (since the ehiem pumps are relatively expensive) and get a
Danner Supreme mag-drive pump from petsmart. both are good, but you'll have to seal the Danner pump as it could leak from the housing if used in-line (a $2 tube of Permatex waterpump housing RTV silicone will do; available at any auto-parts store). its your call...
1/2 inch fittings are less restricting; you may as well get em.
you can find good articles at
Procooling (thats this site d0h) if you look;
Overclockers also has some good ones to check out.