Lewisite I use 36mm unmounted Chroma filters which should work very well with the 2600.
The Chroma filters are great (very low halo); I have two complete LRGBSHO unmounted sets of 36m and 2". The 2" ones are mounted in two separate filter wheels to keep the size and weight down.
Just check the drawings carefully -- there could be some vignetting from a 36mm, depending on the f-number of your OTA.
Chen