M42 combining RGB and HA images a year apart.

I really like this image of the Orion Nebula. Using images shot in 2015 before my camera was astro modified with images from 2016 after the Canon 40d was modified allows me to add some blue oxygen colours back into the image that are missing in the HA image. On my wish  list is an Astronomik OIII- CCD clip filter which block light pollution and lets on blue oxygen light. The new filter should allow me to shoot say 30 subs using each filter then combine them in post processing.
This image contains 7 minute subs and 2 minute subs as the very bright central region is blown out in the longer exposure for the faint clouds.