Stay away from the GWS for combat. It's not selective enough for that use. I have one in a park flyer, and I get hit from other TX's being on at the same time on a fairly regular basis, esp if I get too far from myself or too close to the other TX's

Anything labeled "for park flyers" is probibly a bad idea. They often aren't very selective, and combat is a really tough RF envrionment, with many TX's on at the same time in close proximity.

The Hitec 555 and the HFS-04MG are popular in combat. I run mostly 555's. You'll just have to be a bit creative with the plugs and zip ties to get it to fit. that's what I'd do.

The Polk Seeker 6 will fit. But it's caseless. And I consider it "unproven" in combat. It works great for normal flying though. ("unproven" because it's fairly new on the market, and it hasn't been abused in a season of combat yet. I have one, and several other guys have them, so they are starting to see combat. But I think it's too soon to predict over all reliability)

Btw, one of the issues with RX's that have the plugs coming out the end is that they often have a daughter-board that is soldered on vertically. That's another set of solder joints to break in an impact, and if the vertical board isn't well supported by the case, the mass of the board itself can help break the solder joints in a sudden stop.