I am putting a 400+hp 340 in my car. I am going to rebuild my 727, and my 8-3/4 rear end. What else should i do in terms of keeping the car together?? Will these older cars handle this much hp. I am currently running about a 275hp 340. Any suggestions would be greatly appreciated....

Frame connectors and front discs would be high on my list.

Yes frame connectors are in the works, the disc brakes may have to wait. I am currently in the process of rebuilding my front end with new bushings.

lol 425HP with front 9 inch drum brakes is suicide simple as that.dont waste your time till you have disc brakes and upgrade your front suspension. that chassis was not designed for 425 hp. a fact is a fact

Actually, the chassis is pretty much identical to later Plymouth A bodies except the front frame rails are closer together and the front wheels are two inches further back. I have examples of both, and I believe the early ones are overall less flexible than the later ones.

But yeah, subframe connectors and disc brakes should be high on your list. If it's a factory V-8 car with 10" drums, they are not so terrible, but discs are still a huge improvement.

And if you don't already have HD torsion bars and rear springs, you'll need to upgrade them, too. Good thing is they are interchangeable with all A bodies 1963 through 1976.

What is the inteneded use of the car? If strip with some street, the /6 tbars allow the front to lift nicely. If street with some strip, then upgrade. Just because you have 425hp doesn't mean you have to upgrade the brakes. HP is irrelevant. Its trying to stop that becomes the issue. If you have 150hp 273 and your doing 90mph or you have a nitro burning 800hp stroker small block and your doing 90mph, its going to take the same amount of time to stop (or try to). Discs just make it safer to stop faster. Funny how people always want to make the car faster first, then worry about the stopping part. Not saying th OP is, just something I see a lot of.

The car has 10" drums on it now. The car will be run on the street. My other engine was getting tired and this engine fell into my lap cheap. It was originally a V8 car.