I know a big cam @ .050 is needed to get the flat tappet to "ramp up". Then there's poor flowing cylinder heads that need big duration to fill the cylinder. Mean while you're running into losing torque with going bigger @ .050. Torque is what's important for this combo, and very critical for a heavier car. Those heads are pretty dang good actually. Yeah they're still a little small for the cubes, but I have friends running combinations like this with less flowing heads. Since the heads aren't a ootb 440 source head that only goes 250ish cfm I would lean towards a cam that's in the 260s @ .050 and go for as close to .700 lift as possible. You can go with the 875 lobes so it would be easier on springs. I would use a beehive spring with a 875 lobe combo. This is just my thoughts and opinions. I know some guys on here that are very knowledgeable, and have a good idea on what works. I know of a cam guy that can really get you a nice set up going. He would probably recommend something close to what I am already saying but he has all kinds of other tricks, and details to the cam specs that plays into it.