The pic below shows the older original "Mushroom valves" and split guides on the right and newer 8BA one piece guides with Chev small block valves on the left. Completely interchangable in 21 and 24 stud V8's. The older valves had a 5/8" stem and the mushroomed head required split valves. There was no provision for adjustment, this being provided by grinding down, or building up with braze, the head. Time consuming! The later 8BA engines ('49-'53) used valves with 11/32 stems with a straight sided head which allowed the use of one piece guides and conventional retainers. The valve dimensions are also the same (very close, anyway) as Chev small block 1.5" exhaust valves. This means you can find a wider range of valve suppliers than if you were just looking for original Ford valves, and have the option of using stainless valves (as pictured) to overcome the problems with unleaded fuel.
The adjustable lifter pictured with the new valves is highly recommended and made by Mike's Sidevalve Supply in Adelaide, South Australia and also available through his US distributors,
http://www.flatattackracing.com/