Most of the dies from the 28 ga. 266 should transfer over to the 366. But, you might need to supplement. I thinking the powder and shot drop tubes would need to be added. Maybe the wad seating ram. What do you plan to do with the 266 once you strip the dies out? (hint hint, but must wait until you get to 50 posts to discuss further). I'm also thinking because the shell plate of the .410 is so thick, you would need some parts for the auto-advance pawl to bring it down to the level of the 28 ga. shell plate.

 

You can install a 28ga die set and shell plate on your .410 366. You will need the 28ga shell plate & ring, and the regular advance pawl as there is a different part number for the .410 advance pawl. Also because of the thickness of the .410 shell plate, the shoulder bolt and spacer for the pawl are different. You'll need find numbers 92, 94 and 95 from the parts list in the manual. If you don't want to pay Hornady, hang out on ebay, occasionally 28 ga die sets are listed.
The 266 sizer and deprime, pre-crimp and final crimp will work and the powder and shot drop from your .410 366 are the same as in the 28ga die set. You will need the finishing 28ga taper crimp for the 366. The 266 primer seater is hollow, but you can use the 410 primer seater punch from the 410 366. You'll also need to get the 28ga wad guide & fingers from the 266. The 28 & 20ga 366 wad rams are the same but you can use the 410 wad ram.

 

I have found a tool head for 100$, and a 266 die set for 200$.
I have a lathe and mill, so can probably make any missing parts, I think.
Even the shell plate, but would perfer to buy that.

for 12 ga I use a ponsnes warren 800b. No support really for those.
anyone know if the 800plus or ls parts interchange on the warren press.

 

I have found a tool head for 100$, and a 266 die set for 200$.
I have a lathe and mill, so can probably make any missing parts, I think.
Even the shell plate, but would perfer to buy that.

for 12 ga I use a ponsnes warren 800b. No support really for those.
anyone know if the 800plus or ls parts interchange on the warren press.

I would start a separate thread for the PW question. The PW people will not be looking at this thread.

 

What finish crimp does the 266 use?

 

None.
The finish taper crimp is a feature of the 366.

 

It must have some finish crimp?

 

Not really. It's basically just a cone-shaped crimp starter that puts a rounded edge on the crimp. Not really necessary.