Don't waste your money, just put a cp roller in your sp grip frame.
OTB = £60 if lucky!
I-Frame = £50+ add £25 for the dm4 trigger
CP roller = £25 just drop in.
Spend that money you saved on a ndz rip valve / hammer assembly / lpr / was board and you'll be laughing.
OTB frame is my fav of the 2 though, but they are an aquired taste, so I'd try to have a go before choosing any of the above.