Chromoly steel frames are great. Ever heard of Reynolds 531? That's chromoly, and possibly the most famous and recognizable tubeset in all of cycling history. What I'm saying here is that chromoly frames are awesome, and some are deemed better than others. Some people claim that Columbos SLX is very stiff for climbing, and that Tange 2 was a great Japanese shot at producing with very similar riding characteristics to 531 -- nice and smooth.

How much is this custom build? Lugged or TIG? There are a lot of very very notable steel framebuilders still in business today and it's worth doing some research.