I totally get what you are trying to accomplish. A car that is constantly bucking and chugging ends up being a car you never drive. I am full in on building cars that can be enjoyed on a daily basis. I just think going to a 351 block is more academic than practical. If you put the same heads on a 347 with a 114 lobe sep cam, I think it would come out about the same; or at least no noticable difference. There is a mountain of costs and headache saved by using the factory bolt in block. 351 swaps nickel and dime you to death if you want to run a perfect street car. Motor mounts, special headers that don't fit right and scrub on every speed bump, hood clearance, intake pipes that don't fit, oil pans that hang below the K-member, an AC compressor that hits the battery tray or clutch cable, etc, on and on. Not to mention the costs, special link bar lifters, special distributer, special lower intake, etc, all the other things mentioned as merely hassles. This is just my opinion, and I don't think going with a 351 block is a terrible idea. I just think it will need more swear words, and take many more hours and months that you are not driving your car.
Kurt