Oops. Sorry about that!
I would not want to take away your business!
There is another thread on here about a gent who carved away a substantial portion of his SWVE frame (cannot remember if it is a 9 or 40), and fabricated his own take down plate from aluminum.
I am not sure about that, but on the Glock, it is used to lock the barrel and must be placed in correct orientation after removal. I thought perhaps it was a stressed part and therefore might need to be steel having plenty of support from the sides of the frame. I always wonder about this stuff, but perhaps I should just let it go so you have plenty of "defective" SIGMAs to buy, fix and resell.
I have a VE model in .40 cal that I'm waiting on a frame for. The previous owner took too much away from the frame, and it can't be saved. I may just use it as spare parts for other ones I pick up.
I like these guns...very simple with an easy to understand firing system. All too often, people think they know what they are doing when trying to modify them, but ruin them in the process. Granted, these are inexpensive handguns, and they are designed to be cheaply manufactured, but there isn't much that can be done to improve them, because of the design.
I carry one daily, concealed or open, depending on the weather. I know that each time I pick ut up, it will fire properly. I know that I can trust my life on it to operate as designed...which is better than my 1911's. With the exception of my AO 1911, which is a true mil-spec version, I wouldn't trust them to do what they are supposed to do, because I've modified them so much. The VE versions are perfect, if not a bit too wide. They are a great handgun, perfect for personal defense, and were priced, much like the SD line, in the range that most homes can afford one.
Perhaps one day someone will eventually come along and design an aluminum trigger for the Sigma/SD versions, but I doubt it. The cost to develop and test them would be so high that the average owner won't put the cash out for the improvement.
I'm currently working on an the housing for the sear block trying to cheaply insert a .015" piece of stainless steel so the sear block rides on steel instead of plastic. This is where the gritty trigger comes from. No amount of polishing the transfer bar will improve the feel of the trigger. I'm also messing around with a larger diameter pin to connect the transfer bar to the sear block, in hopes of lessening the trigger travel. All of this takes a lot of time, and the demand for the improvement is low...for the average owner.
In the end, this isn't a weapon that is highly sought after, isn't a weapon that is cheaply improved upon, but is a very reliable handgun that will work each time if left alone.
As long as there are people screwing around with them, I'll be able to repair them and sell them rather cheaply.
Shoot. I didn't even pull my finger out of joint pulling the trigger. 
