[BGCarrera32]

I have a 3.2 to 3.4 conversion, 964 cams, 98mm wedge dome Mahle single plug...

Using 1.63" headers. Keep in mind this is also the factory heat exchanger size. I wouldn't go smaller.

Everything I have read and searched through indicates that 1.5" is too small for this setup.

Now that said, I wouldn't turn right around and sell my 1.5" SSI's either. A 964 is a pretty mild cam, and the performance gain with a header is said to be negligible anyway.