Fluidamper uses the same balancer for FE and 385 series, it includes a spec for shortening the spacer.

Some late ‘63 and ALL ‘64 non-427 FE blocks have those extra webs and cross bolt bosses.  All of those are two bolt motor mount blocks as Gene stated.  The later blocks with no cross bolt bosses and four bolt mounts are also two-web mains.  I’m not sure what they were thinking……..(Ford that is).  Those “extra web” blocks are not exactly like 427s.  There is one main on each side that only has two webs, and the thickness of the webs, and the overall thickness of the main bulkhead is not as beefy as a 427 or a 3-webbed 406.  They are also not as “heavy duty” as a CJ or 105 three webbed block.  I would have to believe that they are still a little bit stronger than a “regular” two webbed block, which were made before and after the 63-64 run of those different style mains in non-427 blocks.

They are not any thicker in the cylinder walls than any other 390 you will find.  I do like those blocks.  I am building a small cube twin turbo engine for a ‘64 Galaxie with one of them.  I have always been impressed with all FE parts that come from the 63-64 years.  I think the company must have been in a good position then.  427s came, High Risers came, and Cammers got designed during that time.  My opinion is that they were more interested in making a good product then.  Something happened  “upstairs” by ‘65.  Yes, they continued to innovate and make neat stuff, but it was all done cheaper and thinner from ‘65 on. 

Side comment…….there were some ‘63 HP 427 blocks that were cast thicker everywhere.  You won’t really notice it unless you see one right beside another ‘63 block, but the head bolt bosses, mains, and cylinders are all thicker.  Some HP 406 blocks are also thick “everywhere”.  Some 406s are the same cylinder bore cores as 427s, but not all 406s are like that.  They did all kinds of stuff.  I wish we had a diary from someone who was in on the thought processes.

badass car

This is a WP170U pump.  It's brand new, I bought it for my Tunnel Port last year, but didn't use it.  I don't have the box.

This is $573 at Summit.  I'll sell for $475 plus the ride.