N6304F, sn 337-0304 is listed in the FAA database as a 1966 337A. It's currently registered to an individual in Ohio. The FAA records list its power plant is an IO-360.
I've seen the single engine Basler conversion (N337BF) at Oshkosh a few times. It’s called a Spectrum SA 550. It uses a 1978 airframe. The registry says this is a P&W PT6A-60A power plant.
There's also a picture of one of these (which is no longer in the registry under this N Number) on Peter's old site at (sadly with many broken image links):
http://www.skymaster.org.uk/spectrum.asp