I searched the internet for aluminum filler necks and found some in England,
but while looking through my repair manual I found a pic of a bolt-on
plastic flange mount filler neck. This is shown in the pic "rad cap filler
neck". Can somebody out there tell me if this is just a mount for a filler
cap or if it is for a pressure cap? Can I also get the dimensions of it with
& without the cap.
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Hi Todd,

The plastic neck in your picture looks like a pressure cap attachment, since
it has an overflow port.  Why would you want plastic though?  

I must have misunderstand what you were looking for, because it seems like
it would be easy to get an "aluminum radiator neck".  A Google search turned
up a few good hits.  Seems like you could just wander down to the local
radiator repair shop, and they would either have replacement necks on a
shelf. At the very least, a call to any custom radiator shop should get you
one.  

One example
http://www.perma-cool.com/Catalog/Cat_page37.html

Something else to think about is getting a neck in a good cap size.
Everyone looks for high pressure caps, and these don't exist in all sizes.
I would make sure there's a nice high pressure cap available for the neck
size you choose.

Good luck,
Rusty