I believe this is the same question posted on "For B-Bodies Only"?

PSH, let me know if this info is correct?
Engine is a stock 74 400
Cylinder heads are stock and sent to AeroHead to be rebuilt with the larger 2.14"/1.81" valves, and hardened seats. (No porting or bowl work.)
Car is the '74 Road Runner (likely 3,900+ lbs), stock converter, 3.23:1 rear gear.
I don't think tire size was listed, assuming about a 26-27" tall tire?
Assuming a 235x60x15 tire of 26.1" height, 3.23:1 gear, no converter slipage, then RPM at 60 MPH = 2494.7 RPM, at 80 MPH = 3326.2 RPM, 100 = 4157.8 RPM

The Sealed Power stock 2-bbl replacement cam #KC327 specs are 206/209@ 0.050" duration, 0.434"/0.431" lift, 113 LSA.
From the '71 Factory Service Manual, the 2-bbl cams is 260/268 advertised duration, 0.425"/0.435" lift, 113 LSA, Intake open 18 BTDC, Intake Close 62 ABDC, Exhaust Open 68 BBDC, Exhaust Close 20 ATDC, 38 degrees overlap.
To get those valve events, the cam would need to be installed 112 centerline.

Engine numbers:
Bore = 4.340" Stroke = 3.380", Rod Length = 6.358", Block Height = 9.980", Piston compression height should be 1.812", flat top, no valve relief volume.
This puts the piston 0.120" below deck at TDC. Displacement is 400.01 CID.
Assuming a 0.020" head gasket of 5cc volume (4.410" diameter), and an 84cc cylinder head volume, then compression is 7.94:1
Using the FSM advertised duration numbers to calculate dynamic (effective) compression = 6.31:1 This should be about 119 PSI cranking pressure at sea-level? Using the sealed Power KC327 cams 0.050" numbers = 7.40:1 Dynamic compression ratio. I don't have a pressure conversion for 0.050" dynamic numbers?

I recommended the Hughes Engines SEH1620BL-12 cam, 216/220 duration @ 0.050", 0.495"/0.503" lift, 112 LSA.
Hughes shows installing on a 108 centerline, but installed at 107 cl will give the exact same intake closing point @ 0.050" as the KC327 cam installed at the stock 112 cl. This means the dynamic compression calculated at the 0.050" lift numbers would be the same.
In theory (based on effective/dynamic compression, but not accounting for overlap) the larger cam should not give up any low end power to the smaller cam, and then make way more power through the RPM range.
Here are the numbers side-by-side:
CAM KC327 SEH1620BL-12
Intake Duration @ 0.050" 206 216
Exhaust Duration @ 0.050" 209 220
Lobe Seperation angle 113 112
Intake install Center Line 112 107
Intake Opens (BTDC) -9 1
Intake Closes (ABDC) 35 35
Exhaust Opens (BBDC) 38.5 47
Exhaust Closes (ATDC) -9.5 -7
Overlap (0.050 duration) -18.5 -6