Hello! I'm working with @FreeThinker of the Interstellar Extended mod to try and get his antimatter engine spacecrafts to be more accurate. Primarily, we want to make sure we have the correct exhaust ISP and reactor output for an antimatter reactor. We're looking at beam-core specifically, but while we are at it, looking ant anti-matter catalyzed fusion or being open to  even more efficient alternatives would be great.  Here is the mod forum link (you can find the mod itself on CKAN)