Help! Heater Core Mystery!!!!

Greetings! The heater core died in my '96 SC 3.1. I tore everything apart to get it out, and now every parts store I go to sells me the incorrect part! The problem is the old core has 1/2 inch diameter outlets and the new one has one 1/2 inch outlet and one 5/8 inch outlet(it tapers down to 1/2inch tube). there is no way the 5/8 outlet will go thru the casing and the firewall! Also, the tubes look like they branch off the left making hose hookup next to impossible on the engine compartment side.(old tubes come straight out into engine bay) Even the gm dealer part has different sized tubes! ARRGGHH!!!!
Has anybody else run into this problem? Help!:banghead:

The AC-Delco part number is 15-60066 (GM#52470156) for your application. Here is a link to the AC-Delco picture of the part:

http://198.208.187.182/internet/ViewPartImage.jsp?acdelcoPartNumber=15-60066

I have never seen a GM vehicle with the same size inlet and outlet hoses, so that is odd. I've done a couple of these, and I believe the pipes can be rotated to ease installation and the larger pipe needs to be "convinced" to go through the firewall insulation (due to how it tapers down). They give you the new straps because the replacement may be slightly thicker than the OEM, necessitating new straps for mounting purposes.