Old heater core looks fine, doesn't seem blocked if I blow air through it. Was it bypassed due to a leak or something else? Had the new one on hand so I replaced it anyway. I suppose I'll find out if it was something else haha.
Old speedometer cable out and replaced. This took a little more work than I expected. The cable is clamped to the body in 4 places, and the grill had to come off to free one of them.
On my van, the speedometer cable is routed through a small opening behind a pair of brake lines and the frame rail. There is not enough clearance for the threaded transmission end of the cable to pass through.
If I had to do this job again, I would completely remove the old cable, then feed the new cable from the bottom up, passing the speedometer end through the small opening behind the brake lines, saving the battle with the old firewall grommet for last.