How realistic is this budget built ? 400hp 318

well;
IMO
400hp from a 318, normally aspirated, won't be cheap, nor will it make a sweet 3400 pound DD. Nor even a decent week-end warrior.
And since we are not in the racer's forum, I gotta say; why in the heck would you even think to build such a combo?
As you know, horsepower is a drop-out term we get by multiplying torque times rpm. So the only ways to increase horsepower are with more torque and/or more rpm. annnnnnd the 318 is quickly torque limited, so that just leaves rpm.
for a street car;
And when you go the rpm route, you quickly trade away bottom-end for top-end. And so in comes;
the hi-stall or clutch, in an effort to find some decent take-off power; and
the rear gears to get the engine up to it's operating rpm; and
the close-ratio trans to keep it on the pipe.
But as a streeter, what you end up with, using 3.55s and an automatic; is a one-gear to 60 mph car, with a sortof rubber-band gas-pedal, that needs to gas up every couple of hours. But hey it goes hi to mid 12s in the quarter, maybe better with a racing suspension.
To be clear;
I am not a 318 hater.
At the 400hp level, it's a logic and budget argument.
As to logic;
It's just that being 13% size limited as compared to a 360, she needs more cam and/or head to make the same power, trading away a lot of bottom end, which is where IDK, say 95% of a streeters life is spent.
As to budget;
by the time you get it built, the only thing still original will be the block, maybe the crank, the timing cover,and maybe the valve-covers. And now with additional costs of; a hi-stall, the rear gears, and the combo wants more than a 3-speed auto, more even than a 3+1. It really wants about 5 gears......... And don't forget, all the support systems, such as fuel, ignition, and especially cooling..... money, money, mo money.
Guys say it costs more money if you have to buy a 5.9 core. IMO, the core cost is the least of your worries.
The 360 falls together at a very favorable street package, right around 330/350 horsepower. It can run the 318 TC and 3.23s and a TF trans and you instantly have a 12 second potential. With the addition of a good alloy head and matching cam, the power can easily run up to 400 very streetable horsepower; and with the right combo, will get similar or better than 318 fuel economy, on the hiway.
I don't get the fascination of comparing a 318LA dinosaur design that started life over 60 years ago, to what is found in the 5.0 Mustang, which is only vaguely related to it's ancestor.
If you wanna be quick, on the street, with a 318, yur gonna have to start with the chassis and powertrain from the bellhouse back. It's quickness will come from Torque-Multiplication and light weight. Then build the engine to work with the gears.