I've got a 45acp upper with FF tube and I want to replace the tube with standard car handguards. Will standard car handguards fit or is the bbl diameter too big? Newby question...but I'd like to know before I buy a set.
Also, what type of tool do I need to remove the FF tube without busting it all to crap? Strap type pipe wrench?

I don't know what type of free float tube you have mounted on your upper so I can't help you there.  I assume that the D ring has been removed and the FF tube replaces it?  Maybe the big scary lookin DPMS tool has a doohickey on it that will help?

By the way, a standard CAR-15 forend WILL fit on the Oly .45 upper.  Mine came that way when I bought it off the EE boards.  I prefer the M4 handguards, however, because they are so big that they bring the .45 barrel back into proportion with the rest of the gun.  With the standard CAR-15 handguards the barrel will look way big and the handguards will look way small.  Plus the heat shields are nicer on the M4 handguards.

Do I need a special Delta ring or endcaps for the M4 handguards? Are they non-standard in any way?

Yes it will take standard handguards or the M4 hanguards - not 'special' parts are needed - just the standard ones.