Hi, I have no car to compare but my 70 challenger, 383 with 220/226 @0.050 cam, 440 heads, KB400 pistons (domes), DP4B, HP manifolds, stock 727, stock clutch fan, holley SA 770, MP performance distributor and orange box, msd blaster coil (mounted in front of carb) + 0.25ohm ballast; has nice power and torque when engine is quite cold.
During first 10 minutes after firing up runs like a raped ape, melting F70-14 in 2nd gear... but when engine is warm it runs noticeably weaker. No signs of any malfunctions but it is not as strong as during the first 10 minutes. When it is hot outside - 90 F and above it seems car loses 20% of power.
Compression is 150-160 and even. I have no O2 sensor to check AFR but no hesitation, no stumble, no bogging while drive be it cruise, be it WOT.
Timing is 20 initial and 36 total. Vac 17 in N @800, 15 in D @700rpm.
I changed the jets to 71 front and 74 rear assuming the carb is too big but this made no difference.

Check the distributor , the pick up coil in those distributors is said to have issues when the engine gets hot.

I'd also look into something better than the orange box , old outdated design .

First I'd try & pin it down to either AF ratio or ign. I'd richen the pri jets significantly & see what happens. 4 or 5 numbers maybe . I ain't sure how far but make a very big jump & richen it way up for a day just for diagnosing

I understand the advice conc. distributor but jetting the carb up? I thought it could be too rich already as cold air is denser. Why do you think jetting up can help?
The engine operating temperature is perfect - 180 deg to 200 when on motorway at 4000rpm for longer periods.

Any chance you're experiencing vapor lock ????

If this isn't a newer (tight) motor, I would expect it to be ignition. Electronics whether it be condensers, coils, ignition modules, etc., tend to worsen under hot conditions.

Check your leakdown hot and cold and your cranking compression hot and cold. Mine loses cylinder pressure when it gets hot, im pretty sure mine is rings. It is noticeably more crisp when cold then as it gets warm it begins to sound like a low compression motor.

You need to jet up, those carbs are lean out of the box. Put 75s in the primaries, 78s in the secondaries, and report back. That jetting worked well on my stockish 440.

Ok, will enrichen the carb however this is almost stock 383 not a 440. Also the plugs show a rich mixture - but that can be misleading as I do almost only city miles.
Distributor may be the culprit but I have no spare to swap.
Engine has 2000 miles and I always measure compression when hot.
I have a spare ignition box (stock blue one) can swap it to give it a try.
Before resto that engine had 7.4:1 CR so I know how a lo comp 383 drives. Mine loses rather some torque than power.

PS
It's not a vapor lock, I can spin it to 5 grand no issues, no fuel starvation.

If not electrical it could be an internal clearance condition. Do you know what clearance the piston to cylinder wall is, and more importantly, what it is suppose to be? If the clearance was too tight when assembled, the piston expands when hot and gets tight in the bore, killing power.

make sho the exhaust is flowing well, friend had a bad muffler once down 100 hp on dyno.

I bought the distributor in 2009 and it's the new electronic unit (mallory?).
Engine was assembled on the lose side so the piston to wall clearance shouldnt be an issue.
Exhaust is 2.5in + super turbos, not most free flowing but the intake is close to stock too.
Swapped the box but cant drive the car today - hail and storms here ;|
If there's no change I'll change the jets.

Good advice on timing - didnt know the box moves it

One other thing is do you have a fuel return line? Others have had this problem because fuel was heating up and causing lean conditions at the carb. Also maybe a carb spacer to help with dissipate heat.

Finally had time to test drive. 85F heat, some traffic and bingo - even hot still fries tires! What I did is replaced orange box with a ... $19.99 NAPA blue box. No other changes. Timing is 20 initial and 40 total now but no pinging.
Time to get a revenator... sad it's sold out everywhere.

PS
I don't have fuel return line - fuel system is totally stock. I have a 1/2" phenolic spacer under the carb but I still have to crank several times to fire up the hot engine - fuel evaporates from the carb.

No the time for Pertronix or point system throw the orange box in the trash

Is it possible to put a pertronix conversion kit into the modern distributor (from the MP kit w/orange box, already with magnetic pickup)? Or should I buy another stock points unit at napa/rockauto ?

Install a Mopar chrome box...

Just my $0.05...

Don't want to buy another MP crap, also don't want to put MSD system as I have the stock tachometer in the dash. And I like it.
The orange box was giving hard starts, rough idle and power drop when hot - none of these with a cheap replacement noname blue box!

If it can be done (please tell me!) I;d like to go with pertronix and MP distributor (modern type).
if not I'll wait for revenator and use the blue box (that is UGLY in an R/T) now.