Sure, I would agree with that. There are several cases of Gentiles being in saved throughout the OT. Caleb, Ruth and Rahab were Gentiles but chose to live under the OT legalistic system. But this system was imperfect. Naaman was also a Gentile believer but asked forgiveness for not being able to follow through with the laws (such as going with the king into pagan temples).
I wouldn't argue that the beginning of the church started at Pentacost. But it evolved. It took 10 chapters in Acts to get to the inclusion of the Gentiles.
That would make you a... dispensationalist.