GJ,
Here are some other thoughts on replacing those gages - although these are "approved", I'm not sure the 337 in necessarily included.
The JPI 711 can replace the factory CHT, TIT and Oil Temp. This info is hard to locate on their website - but you can find it in “Downloads” in the 700/711/800 manual pdf.
www.jpinstruments.com
Electronics International (
www.buy-ei.com) has a number of primary instrument replacements. RPM, MAP, CHT, EGT, Oil Press & Temp, Volt/Amps, TIT
Shadin's Digiflo can be used to replace the stock fuel flow gage.
www.shadin.com/ff_digiflo.htm