I searched [ the Internet] for the 3D CAD model for the AnyCubic Kossel Linear Plus frame - the #1 important thing for me was keeping unmodified the bed diameter. The #2nd important thing was the type of the tower rails - specifically, their thickness. You have to decide what you should keep [inherit] from the old printer when creating a new printer.
Also you must find online the CAD models for the Delta Smart Effector.
Using a CAD program to edit ensemble frame+effector, I kept the following elements as unmodifiable :
- the bed diameter = 240 mm, as I absolutely did not want to order a new heated bed -- that was inherited from the Kossel Plus printer -- that is important since such a bed is kinda hard to find -- well, maybe not that hard if you are willing to wait for another 2-ish months of waiting for the Chinese guys to ship 
- the tower rails -- those are the [noname] MGN12H rails that came with the Anycubic Kossel Linear Plus printer -- they are kinda easier to find from a retailer closer to you, not necessarily China only.
Eventually I designed my own custom frame using custom 2060 extruded aluminium frames for the towers. That required custom-designed delta corners, as I wanted to keep my 240mm bed.
That is an chicken-and-egg problem.
I had to keep alive and running the original Chinese Kossel printer to print all the necessary parts, until I was sure that I am well beyond the no-going-back point. Because once I decide to dismantle the Chinese Kossel printer, I cannot be sure, not in 1000 lives, that reassembling it would result in something that would print 1+1=2. Because China. So, the printer upgrade process is one-way.
OK so using the CAD program I calculated that I need 288.14 mm Haydn arms.
Then I went shopping online for such custom-sized Haydn arms.
Most offers I've seen online were for pre-built 360 mm Haydn arms, but that was not good for me because:
- arms longer than 288.14 mm will worsen my delta printer precision
- also arms longer than 288.14 mm will lower my printable height too much, should I have towers' height restrictions;
- arms shorter that 288.14 mm will shorten my printable diameter too much below 240 mm.
So if you are into building your custom delta, you have to find a way to get precise-built rods. Haydn arms are precise-built. My 6 Haydn arms were shipped like so:
- 4 arms of 288.14 mm
- 2 arms of 288.15 mm
So 0.01 mm difference, that is really close to perfection.
If I would've tried to build my custom arms, chances are that I would've made mistakes that would've been led me to rebuilding the arms again and again -- eventually leading to an overall cost much greater than what I would accept.
The original Duet Delta Smart Effector ships with and e3d v6 0.4 mm hotend.
The migration path from the e3d v6 to a e3d volcano is easy. You keep the Duet Delta Smart Effector PCB. You just have to sacrifice 1-ish centimeter reduction in printing height.
My final configuration is as follows:
- original 240 mm heated bed inherited from Anycubic Kossel Plus printer
- custom frame with custom 3d-printed delta corners
- custom-length Haydn arms (4 x 288.14 mm + 2 x 288.15 mm)
- Two Duet Delta Smart Effector: a) first one for e3d v6 0.4 mm hotend, and b) second one with e3d volcano 0.8 mm.
- Duet 3D wifi motherboard
- Duetx5 (I want to add separate dedicated flying extruders for each of my two hotends)
Regards