Why not use retrofit rollers lifter and a cam button? You can also use an internal balance rotating assembly for the 400 and reuse your neutral damper and get a neutral flywheel.
Originally Posted by DoubleVision
The roller cam in the 400 is out, why is because the depth of the roller lifters is
True but there is way using shorter V6 roller lifters...I did it for a SBC 406 build with 7000 RPM redline and made a video too. I choose stock lifter becasue they are much lighter than retrofit link bar liftes but in a low RPM truck motor link bar retro lifters will suffice.
Small Block Chevy Gen1 SBC roller lifter retrofit - YouTube
considerably taller than the flat tappet blocks. .