Standard tooth count is 153. High performance (high compression) BBC were 168 count. Not very common especially with a TH350 behind them. Yours is more than likely the 153
Can't speak to flexplate/TH350 combo's (got none) but my 350/TH400 has the 168 tooth plate and the staggered mount starter. But then again, it's a HO 350 out of a 68 Camaro, so maybe they were a tad different than the newer ones.