Tom;
 Just a recomendation that you purchase and install a complete new Racor fuel filter assenbly (perhaps a type 120) rather than trying to piece together the old one. The suggestion comes as the result of an experience I had last season where the paint on the filter assembly was being broken down by the diesel fuel oil and caused an air leak into the fuel system at a seal point. It took forever to find but Ithink you would be better off with a whole new assembly. Might be less expensive too. ​
https://www.defender.com/product3.jsp?path=-1|311|2349059|2837510&id=133972
YMMV.
 Bill

Tom;
By the time one gets around to buying a new filter and bowl, you are at the price of a brand new Racor Assembly. I replaced my old Racor with the unit indicated below paying around $100.00 + or -  with commericial discount at Bacon's in Annapolis.  The filter uses a plastic bowl as only Coast Guard inspected boats in commericial service are required to use metal bowls and you can use the old elbow fittings.
The Racor filter coding is as follows; The R-20 'S' filter is filtering at 2 microns; The R-20 'T' is filtering at 10 microns and the R-20 'P' is filtering at 30 microns. Recall that the finer the filter you use, the more pressure is placed upon your fuel pump to get the fuel through the filter. That probably equates to a shorter life for your fuel pump.
I use a R-20 T filter at 10 microns since the fuel filter mounted on the engine is 10 microns and my fuel source  is usually reliable. The injectors will usually tolerate 10 microns. Just remember to turn the fuel off at the tank before starting this project. .......Bill
https://www.defender.com/product3.jsp?path=-1|311|2349059|2837510&id=366095

I've used several from eBay like this one.   They have all worked just fine and at under $10 hard to beat. 

https://www.ebay.com/itm/For-Racor-RK30475-Bowl-Kit-Fuel-Water-Filter-Separator-320R-RAC-01-S3213-S3214/233404298837?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D783b4eef5ed34cd0a9c0841b609ce65b%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D233404298837%26itm%3D233404298837%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Aa9f36e61-0d4c-11ea-ab77-74dbd18040bd%7Cparentrq%3A9422faed16e0a99c67fa2c08ffe71983%7Ciid%3A1
 

Having had engine failure while underway, due to tank contamination, low fuel level, and rough seas, I have thought about installing Racor's dual filter kit to allow you to switch over from one filter to another while underway, if need be.  Has anyone done this?  Is there room?

Not Racors prebuilt dual but much cheaper. I did a write up on this over a year ago.  Check the back issues of Mainsheet.  (In members only section).   

in addition to dual filters I used dual lift pumps, so I can polish fuel if necessary   

note Racor 500's do work well but I feel are overkill for our small engines.  You need to go thru a bunch of filters to make the high initial price of the unit make up for the lower cost of the consumables.   

Les