≅375 to 400 net SAE horsepower can be achieved with a very stock engine. With D1ZE heads you'll need to compromise and consider using pop-up dome pistons. There are better headers than the big bore headers too.
John Kaase was once asked what it took to make 400 bhp with a 351C, he replied "pull two plug wires".
We can cover the topic when ever you wish privately or in public.
Check this out:
Starting point: 1972 Pantera, ≅ 286 net SAE horsepower.
Step 1 unclog & de-smog engine:
Add square bore dual plane intake manifold (factory M code manifold is fine).
Add a performance calibrated 650 or 750 cfm carb with annular boosters.
Raise compression to ≅ 10.2:1
Advance factory CJ camshaft 4°
Subtotal ≅ 350 net SAE horsepower
Step 2 perform the universally desirable emendations:
The Cleveland has three known failure modes, even at baseline rpm levels two of them are worth taking steps to prevent from happening; and there are four recurrent problems which I also recommend taking steps to prevent from occurring. Thus there are six "universal" problem areas in terms of durability to be emended for all engines, all rev limits, all power levels, and all applications.
To summarize the durability emendations: (1) Valve Failure: Replace the factory valves, high quality steel valves utilizing OEM style loose fitting 4 bead locks are OK up to 6200 rpm; (2) Connecting Rod Failure: Replace the OEM connecting rod nuts with ARP p.n. 300-8381 nuts (2 nuts per pack x 8 packs); (3) Low Hot Oil Pressure: (3A) install tappet bore bushings with 0.060 inch orifices; (3B) install a high volume racing oil pan having baffles with hinged doors, a windage tray, and a scraper; (4) Connecting Rod Bearing Wear: (4A) install heavy duty (tri-metal) main bearings (Clevite #MS1010HG or #MS1010VG), fully grooved, with 0.0025 – 0.0032 clearances; (4B) use 10W30 Valvoline VR1 motor oil; (4C) install heavy duty rod bearings (Clevite #CB927) with 0.0022 – 0.0028 clearances; (4D) set the connecting rod side gap clearances at 0.018 – 0.022; (5) The Crankshaft Damper Ring's Position Shifts on the Hub: Replace the OEM crankshaft damper with a PowerBond p.n. PB1082SS high performance “fully bonded” steel damper; (6) Engine Over-Heating: (6A) install the correct Robertshaw 333 thermostat; (6B) insure the brass orifice is located in the block below the thermostat; (6C) insure that the recirculation passage within any Weiand or Milodon coolant pump is drilled out; and (6D) insure the head gaskets are oriented properly during assembly. If there are questions please express them. I am more than willing to explain the reasons behind these "decades old" recommendations.
Spin Balance the Reciprocating Assy.
Install a breakerless ignition (Duraspark recommended).
Have the distributor calibrated with a performance advance curve.
Subtotal ≅ 364 net SAE horsepower
Step 3 "Options"
Aftermarket (or De Tomaso GTS) Tube Headers.
Exhaust System Improvements.
Three Angle Valve Seats
Block exhaust heat from the int. manifold (annular boosters help here).
Subtotal ≅ 410 net SAE horsepower
Its possible to get this far without hot rod parts, unless you consider the improved carburetor and/or headers to be hot rod parts. You mentioned putting a cam in the engine so lets explore that ...
Step 4 - A Point of Convergence
Add a hydraulic tappet cam with ≅ 0.530 gross lift
(requires improved springs and push rods too)
suggested custom camshaft
duration at 0.006 lobe lift ≅ 270°/285°
duration at 0.050 ≅ 218°/230°
gross valve lift ≅ 0.530/0.533
cam is ground on 114° lobe centers
overlap based on seated valve events ≅ 49.5°
This is the factory CJ cam ground with lobes providing 0.050 additional lift.
TOTAL ≅ 440 net SAE horsepower at 6200 rpm.
Equipped with 4V heads peak horsepower occurs at 6200 rpm with gross valve lift at 0.530". That’s right up against the base rev limit. So unless a person is willing to spend the money performing the high rpm durability improvements needed to safely raise the rev limit, it doesn't make sense to install a cam with more than about 0.530 lift. The factory rocker arms are known to cause accelerated valve guide wear when used with high lift cams. So 0.530 lift is a good limit for the factory rocker arms too. AND … with 0.530 lift a 351C 4V engine with a single 4bbl carburetor is capable of easily making 400 horsepower, and 440 is achievable (getting to 440 horsepower may require a bit more carburetor than 650 cfm). It just so happens that 440 bhp is pushing the limit of the factory fuel system to supply an adequate amount of fuel. 440 horsepower is also within the limits of the factory clutch. Engines making 440 horsepower, having no more than 7.8:1 dynamic compression, and rev-limited at 6200 rpm are in no danger of cracking cylinder walls either (as long as they are in good states of tune and their reciprocating assemblies are well balanced). So there's quite a point of convergence for 0.530 lift and 400 to perhaps 440 horsepower. The main ingredients are a performance tuned 650 (or 750?) cfm carburetor, a bump upwards in the compression ratio, a 0.530 lift short duration cam, valve springs, push rods, and exhaust improvements. With the right cam the engine can have good low rpm power, a nice muscle car burble in the exhaust, and be tame enough to drive to work daily. Not too shabby for 50 years old technology.
From this point onward however the dollars multiply quickly.