If you're sure the heater core is gone you can just crush the copper nipples, hack them off so you can turn the ends up for access and then peel the crushed nipple out of the end of the heater hoses. In the 900s, the heater core nipples were caulked to the firewall to prevent water intrusion, which can make final heater core removal a bit more difficult. As I noted in my FAQ article, push the remaining nipples through the firewall from the engine side once the heater core straps are freed on the inside. I've also done this job twice and every time it gets a bit easier if you can only remember a few of the tricks for the stubborn parts and the minimum amount of dash that needs to be removed. That's why I spent all that time during the second one writing that long article so that I'd have something to reference the next time. I didn't have a digital camera, so Ari was later kind enough to add some pics, plus I was working with all black plastic in an all black interior. Regrettably throughout a number of FAQ revisions the article lost some if it's content. That final top screw is the major challenge, but with the techniques listed and a bit of patience it will come. I initially thought about breaking that tab, but that would be admitting defeat.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now