One of the games I play is Heavy Gear (and mainly the Southern MILICIA). I've always wanted to field Rattlesnakes, but for the longest time, I only had the conversion pieces from the Blitz Southern weapons blister (DP9 9066).
To those who don't know, the difference between a Rattlesnake and a Jaeger is that the Rattlesnake has a smaller head mounted on a larger hatch, and that it is equipped with a medium rocket pack.
The biggest question I had had with the plastics was how well the old conversions would work. Simply put, it's not a clean fit. I had to slice off part of the hatch, because the alternative was to shave off part of the Rattlesnake hatch. I will need to use some kneadatite to fill in the gap, as the Rattlesnake hatch is bigger.
And the MRP just needs some pinning. Drill a bit into both the hull and the MRP's socket and it should be fine.