Got the replacement part back from the local fabricator. Cost $150 instead of $230, came back in a few days instead of a month.
Barely managed to wiggle it in and get a wrench on the screw heads under the blades. I expect I would have had to pull one if they were much farther out.
Then it...
I finally got that floor plate out, which was a nasty job. Stuck screws, screws that just spun and then rounded the allen heads.
Once I finally drilled the last of them out, the thing was about 1/4" too wide to come out the back. I had to slant it up and push it forward under the drum and then...
I believe that's the brand new cutter bar, but it's possible it's the back of the newly sharpened blade.
The round face is the top of the enclosure that feeds into the drum.
I bought a 1996 Altec DC 12 with ~1200 hours on it dirt cheap on Craigslist.
It wasn't feeding well, and the cutter bar was cracked, so I replaced the cutter bar and sharpened the knives. (That was a lot more work than I expected!)
Now, it grabs the branches pulls them in sharply, cuts them to...