I would build the current 400 motor into a 4.250 stroke stroker motor after having it sonic tested to make sure you end up with at least .150 cylinder wall thickness on the cam side and motor mount sides of all 8 cylinders.
The 400 blocks have a lot thicker main webbing and you can crack the 440 main webs a lot easier than the 400 block
I would and do use either 6.700 or 6.800 good brand long H beam rod to safely make 600+ HP on pump swill
As far as the cam to use I like big ones On the exhaust system I would and do use a 3.0 pipes from the collectors to the 3.0 inlet and outlet high flow muffs.
You need a good converter to work well at the track and driving to the races, I like and do use a good 8 inch Not a cheap one
My first "drag race only car" was a 1960 Dodge Phoenix that weighed 4050 lbs. without me in it, I traded a 1955 Chrysler Fire Power 331 C.I. Hemi and installed into the guys roadster for a stroker 383 motor (unknown the true C.I., I was told it had a welded up 413 crank that had a 4.250 stroke and bored to 4.310 ) that I put a stock type dual 4 barrel set up on that motor. That car ran 12.80 on a set of J.C. Penney 7x26x14 slicks, yes they sold them for a while back in the late 1960s. That was with a stock cast iron torqeflyte and stock low stall converter with 3.73 gears and no posi .
I was very happy with those results
Good luck on your build Make sure and degree the cam and verify the compression ratio on all 8 cylinders