The 427W is pretty easy to build with off the shelf parts. Contact a company like Eagle (
www.eaglerod.com) and buy a complete matching balanced rotating assembly. Follow their instructions and you're done. No sense re-inventing the wheel when companies like that have done all the work for you.
427's generally have a longer stroke than the 408's. That's why the 427 doesn't rev as high - pistons speed are pretty high.
Pick a block that's '74 or older. You can safely bore them out a little bit larger, and they have a taller deck.
As for the roller cam, unless you're putting in a huge cam, there's very little performance differance between roller and flat tappet. I think the test showed that l;ess than about 260* it's a wash.
Older non-rollerblocks can be converted to roller fairly simply. Use a small base circle retrofit roller cam. You'll need to drill and tap two small holes in the valley, and grind a little bit here and there around the lifter bosses. Not a big deal.