PCM engine water pump bypass?

If it's a Ford and using a Sherwood G21 raw water pump you'll want a genuine Sherwood impeller # 9955K
Drain your engine and manifolds first,replace the drain plugs then add antifreeze then drain that again and then replace the plugs again. If you have a heater you must drain that too,I blow mine out with air,and fill that with antifreeze too. The most expensive antifreeze is still cheaper than replacing an engine   
PS your way to early to be worrying about winterizing even though being in Wisconsin your about 3 weeks out

I believe it is this internal passage in the lower thermostat housing,nothing to worry about, it will all drain when all plugs are removed



If your pump looks like this one,it's a G-21. They do have aluminum tags with the model number held on by one of the bolts used to hold the housing together and usually lost



In the reference section of this site are the owners manuals for most of the different engines this one is yours
On page 43 of the pdf file are the lay up instructions,it tells you what to do along with the drain locations.Not sure it it shows the manifold drains but if you have PCM manifolds they are the plugs opposite side of the water hoses that are connected to them. Any ? just ask,hope this helps