You are correct, Ford no longer offers any pushrod V8 engines. However, for all the NASCAR teams, the blocks are customed made anyway. Since they all have the same dimensions (bore, stroke, and bore centers), I wouldn't be shocked if the castings all came from the same foundry.
If OHC engines are allowed, the teams with the obsolete pushrod stuff will be in trouble.
If the rules were changed to allow OHC engines AND pushrod engines, the teams would have to weigh any potential penalties assessed to the OHC crowd - displacement limits, weight, restrictors, etc. and decide accordingly. If the OHC engines had an advantage, then Ford and GM could compete quite well - they both make several outstanding examples of DOHC V8 engines in production, and both have extensive DOHC V8 racing experience (Ford in F1, GM in IRL, both in CART).
Incorrect. Ford Racing offers a whole line of complete warranteed pushrod crate motors, including a 514 ci/600 hp bracket racing setup.
http://www.fordracing.com/parts/search/results/index.asp
Similarly GM Performance offers a new 502 Rat stroker, and Mopar offers the monsterous 526 Hemi stroker (750+ hp).
Psst... don't tell the EPA...