leaking anti freeze onder dashboard

Been a while since I had an 85 but IIRC you can replace that core without pulling the instrument panel. Seems like you remove the screws for the cover from inside the passenger foot well, watch out for the two on top that can be hidden and one that is a stud going into the engine compartment. Clamp and remove the hoses under the hood. Remove the straps and the core. Reverse this to install the new one.

There is a tutorial here with pictures

AKA

I've done an 84 & a 94 S-10 Blazer. It helps to have a 1/4" socket set with extra and/or long extension bars. For me, the bolts that hold the

2 straps on the core itself were hardest to deal with. Don't remove the 2 uppers, just loosen them. I did not remove the ECM, but did remove radio and glovebox. Just loosen the dash itself.

Thanks for the pics

Does anyone know what size these heater hoses are? I am looking to temporarily connect the input and output hoses together.... need to find some type of plastic connector.

3/4" and 5/8" Easiest method would be to buy one of the coolant flush kits that includes T fittings that will fit all the different sizes. Plus when your done it provides an easy way to flush the system. Like this one.