Welcome to the forum, and sounds like a great project. My advice would be to steer well clear of the Dove block. My personal experience with Dove parts has included poorly machined and leaky head castings, substandard SOHC rocker arms, etc. The Pond block is an excellent part; I have one and it has hung in there through various iterations of an SOHC engine up to over 800 HP. Also FYI I have it from a VERY reliable source that Genesis cast iron 427 blocks are coming back soon. The cast iron block would be a better match for your cast iron heads, and should be significantly cheaper than an aluminum block. This is not to say that you can't bolt your cast iron heads on an aluminum block, because you certainly can do that.
For a HP target of 650 or so you can use a cast Scat crank and Scat H-Beam rods with good results. A forged crank would be better, of course, but there are some sub-standard forged cranks out there now so make sure you get any crank checked carefully by the shop that puts them together. A lot of the forged cranks need to be ground 10/10 or 20/20 even when new to get the dimensions right.
My recommendations for a shop are either Barry Rabotnick at Survival Motorsports or Blair Patrick at Blair Patrick Racing Engines. They both do excellent work, and there are many people on this forum and other forums that will vouch for their FE expertise.
Finally, on the MSD the 6 will be fine for your application; on the dyno I've run up to 800 HP with an MSD Digital 6. MSD 7s are killer boxes, but you won't need something that powerful for your combination.
Good luck on the project, and keep us updated on your progress - Jay