Your right, I think machine work may be a bit higher. By the time I got to that part I just threw in some rough estimates. I use a semi-retired machinest and his prices are lower than what seems to be the normal rate. In my notes I did estimate the machine work could be around $1,000.
I have my own cam bearing tool, so I haven't paid to have that done in several years.

The stealth heads have valve springs that are compatable with the cam.

I used two reference sources, Summit Racing and 440 Source. If the part does not mention 440 Source that it was referenced from Summit. The only non-name brand parts from 440 source are the heads, timing set, and Harmonic balancer. I listed 440 Source for some of the brand name parts because they have good prices on those parts. I think shipping on the stealth heads was $50 when I bought mine.

To keep the costs down, assumed the re-use of the oil pan/pickup, rocker system, intermedate shaft,pushrods, distrubitor, plug wires, ignition coil, water pump, valve covers, etc.

I like the HV pump because it gives good pressure at idle, but stock size pump works too.
I quoted using the 440 source timing set. I have this timing set and it is a nice setup, but you could use any 3-bolt timing gear set, even less expensive units. If you look at the parts, these are not the bottom dollar parts, they are higher performance parts than just standard rebuilder parts. You may be able to bring the cost down by using lower quality bearings, piston rings, gaskets, head bolts, main bearing bolts, rod bolts,etc.
The harmonic balancer is a big question mark as to how much to spend and which to get. You might be able to save money if re-using the stock balancer, but I would not trust a 40-year dampner. I have not used the 440 source dampner, so that is a big "?", but I would recommend at least a new dampner, but it needs to be able to accept the stock pulleys (The stock dampner is recessed) because some of the performance dampner like the fluid dampner and ATI will require different depth pulleys.
The ARP main studs are optional, but they add less than $50, and are one of the items that would be difficult to add-on at a later date.
That gets us back the the rocker system. The rockers and pushrods are easy to upgrade by just removing the valve covers.
I also listed the Champion spark plugs from 440 Source. I did that to just try cover all costs, but I prefer NGK spark plugs, just personal preference.
I listed the Edelbrock RPM intake because it works and is easely avaliable new. One issue with running a low deck "B" block is the lack of intake selection. Also, if buying a used intake, you don't alaways know what modifications have been done to it.

Last note, the Stealth heads were chosen because they do have a stock appearance and are inexpensive. If the appearance is not an issue, you could go with the Edelbrock heads for a few $$$ more. You could also do this with stock Iron heads, rebuilt with larger valves, hardened exhaust seats, and ported but that may be even more expensive than the aftermarket heads?

There are many ways to build the engine, this is just my on what I believe is good "bang for the buck"