how do i match up heads with a cam
The question is redundant and impossible to answer. Static Compression, Strength of Rotating Assembly, Type of Induction and Gearing ... etc is what determines Cam Selection - Please read my post and Download the Software with the links I've provided. It will give you much more understanding - Do the Home Work ;o)
PS: The Block Casting Numbers are on the Top of the Bell Housing Boss just behind the Distributor and the Head Casting Numbers are easily read with the Valve Covers removed. Note: The large oval port 820, 781 and 049 Head Castings are great performance heads if you have them. Many Flat top Piston 454's have been topped with Closed Chamber 396 Smaller Combustion Chamber heads to up the static compression.
To top it all of you need to know what the Dome Volume of the Pistons are which requires the removal a Cylinder head at which time you can CC the Cylinder Head Chamber Volume..
The Engine Code written on the PSGR Deck just behind the alternator can supply us with the exact Year and Model the engine came out of and if the motor is stock will tell us info re: piston along with the static compression.
If the motor has a History perhaps the previous owner can supply you with most the information but I personally never trust it.
There are just too many variables in your Question as you require the Specifications as I've outlined above to Select a Cam using Mfgr's Software. Head Gasket Thickness, Distance Piston is down in the Bore, Cylinder Head Volume, Piston Dome, Bore Dia & Stroke, Induction, Dynamic Compression Vs Pump Gas, Transmission, Gearing and what do you want out of your ride are critical factors when choosing a cam.