Air Vents Pouring Water!

If the lower plenum is rotted out around the air inlet standpipes, a lot of people end up doing major sheetmetal surgery in this area. The lower cowl plenum is available new from AMD as well as the upper cowl panel. If your into drilling spotwelds and reusing rust free vintage tin, theres several members here that drill apart dry area cars and sell the steel.

To repair this by replacing a rotted lower plenum you have to remove the hood, fenders, everything off the firewall including brake pedal, and steering column, windshield, and dash frame. At this point you can start removing spotwelds. Being that welding is involved to put it all back together, I also recommend taking the front seats and front carpet out.

The A pillars splice in at the corners with spot welds and lead filler. Just heat the lead with a torch and brush it out of the joints on either side with a wire brush. You can buy a lower plenum and splice in what you need, but as far as you will have to take it apart to splice it, you would be better off just changing it out.

Theres tooling holes that line all this stuff up. This aided in factory assembly, and will still work for a DIYer.

Hope this helps
Matt