I've had a number of High performance 409s, and they were very different from the 340 hp engine. Much bigger heads, radical flat tappet cam, two Carter AFBs, 11.5 to 1 compression, and some free flow exhaust manifolds. The factory rating was 425 HP.

If you want to find out actual horsepower, NHRA used to factor engines in Stock classes. Maybe you can find out what their "actual horsepower" rating was. Just for example, the 426 Hemi was rated at 550 HP, so I doubt that a 340 horse 409 is capable of those kinds of numbers.

I think you will find that it will bolt to your trans, but may have problems with the fit, due to the width of the engine. It is also much heavier than the smallbock, so you will lose some performance there, too.

I would put my money into a 400 smallblock, which is nearly a bolt-in, and you will be able to buy anything you want for the project, such as pistons, headers, cams, etc. I had a friend with a 406 in a '68 Camaro that ran consistant 10s with a Powerglide.