I know wickedatv is not a sponsor here but I bought my 421 kit from them.
Comes complete with welded crank, 115 rods, head and domes, pistons, Athena cylinders and seal kit for $1400.
Mine runs pretty good.
I purchased mine from Roger at Wicked Motorsports.
He machines this area so the stock plugs fit.
Mine went right in.
Price for the kit was good as well with +4mm crank with 115 rods and Wiseco pistons and all seals and gaskets was under $1400.
Hope to fire it up soon.
Hopes this helps...John