I have quite a few of the WDHM shorts including the 400ft ones. The last I purchased was Disney's Greatest Chases. When I''m next off I will post about each of them on here.
As Mats says, the 400 footers usually have 4 or 5 cartoons on each but none are ever fully complete though in many cases they are really well edited just like the T & J Toons are from Walton.
Another favourite 400 foot compilation reel of mine, is A Walt Disney Christmas.
The best Disney compilation reel though, by a country mile, is the Derann 600ft release of "Once Upon A Mouse".
It's a superb fast moving look at all the various era's and sensational work, short and long, of the infamous Disney Studios. A real masterpiece.