Well first off, the retro arms gearbox could withstand springs even higher than a prometheus ms210 (strongest spring on the market), the aluminum (7075 t6 billet) is not expensive for no reason. A simple radius and sorbo on most v2 gearbox shells will yield great results. The jg gearbox is fairly strong as some people run m190 55rps dsg's on them with no problems. A steel gearbox would really be unnecessary when the retro arms would be way lighter and stronger. Aluminum is actually used in most racing engine blocks. As for an sts or shock transfer system, you really don't need one if you do proper radius'ing and sorbo'ing. I usually only recommend sts's to people wanting to run a weaker shell with a high stress setup. You should not experience any gearbox shell failures if you do the precautions that i mentioned. If you do, a lonex gearbox which is virtually indestructible is only $50. Hope this helps, happy building.