Plus and minus to the 440 or 400 block combo.

My preferred engine: The 383/400 block engine is overall less wide and less tall. This means actual room for your hands and socket/ratchet to change spark plugs on the passenger side. Also gives you more hood clearance, which is great. 383/400 block also weighs less, and the 400 block has stronger main webbing as mentioned. More room for header clearance. I personally think they look better also, more compact. Downside, intake selection has less choices, but enough to get the job done. No max wedge crossram, unless you run stage 6 mopar heads.

The 440 block engine has the most selection for intake manifolds, and is probably a little easier to build. However the 440 has downsides: block main webbing is not as strong, heavier, wider, taller, less clearance to work on the passenger side spark plugs (really non existent for #2, 4 cylinders). The crappy clearance issues for the spark plugs/headers, and less hood clearance using a 440 block is enough to really consider building a 383/400 based engine in my book. Note: Small block mopars have awesome spark plug access, way smaller overall size, weight...worth considering a 408 stroker type build.

I personally have based 440 based engine 505 stroker, flywheel dyno'd 620 HP @ 5900 / 620 torque @ 4800, 4.25 stroke/7.1 Rod, Keith Black forged flat top pistons, A&A max wedge cross ram with two 600 cfm Edelbrock carbs, Edelbrock RPM heads, CNC ported by Modern Cylinder Head, Bullet solid flat tappet cam 259/263 @ 0.050, nearly .600 lift, 108 centerline, BHJ balancer, TTI 2 inch headers, 10.5 compression. Never run down the quarter but its super fun and fast enough. Will run on pump gas but likes 100 or 110 leaded octane better with more advance like 35 degrees. 4:10 Dana, with A-1 4800 stall 8 inch converter, and Pro-Trans full manual 727. Installed in my 1964 Plymouth Savoy, street legal and driven often. Yes...I hate changing the spark plugs on the passenger side.