In an earlier Things-Under-Wing post(http://tailspintopics.blogspot.com/2013/06/things-under-wings-f4h-f-4-phantom.html), I provided information on and illustrations of the Navy F4H/F-4 external tanks. It described two different 370-gallon tanks, with the earlier McDonnell one not usually provided in F-4 kits. Jeffrey Kubiak of Hypersonic Models is now offering it in 1/48 scale:
https://www.hypersonicmodels.co.uk/product/mcdonnell-370-gal-tank for more pictures and order information.
Jeffrey recently sent me a picture of what appears to be a third 370-gallon tank that had been brought to his attention by Joerg Stange.
My guess is that this is the 370-gallon tank produced by Royal Jet that is listed in one version of the F-4 Flight manual. An informed identification of it would be welcome. However, it doesn't seem to have been widely used, certainly rarely photographed, compared to the Sargent Fletcher tank.
This is a crop of the picture Joerg identified in his first comment below, which was in Part 2 of First and Foremost (NAVA 3); a high resolution image was kindly provided to me by Angelo Romano. You can order a copy of this excellent monograph here: http://www.aeroslides.com/modelpublishing/book-store.html
Note that the tank under the left wing appears to have a shorter cylindrical section and flange than the Sargent Fletcher tank; it is likely that this is the relatively rarely photographed Royal Jet tank. (The one under the right wing is the tank that was furnished by McAir.)