340 or 408?

Couldn't find a 500+ hp 340 build but here's a little more than you wanted 592 hp @ 7,100/7,200 rpm
460 tq @ 6,000 rpm 400 tq @ 4,000 rpm, 12.5 cr W2 tunnel 263°/268° @ 0.050" solid cam'd 345.

You go a little on everything you get a little less hp.

https://www.motortrend.com/articles/mopp-0205-340-big-block-engine-buildup/

https://www.motortrend.com/articles/mopp-0206-340-big-block-engine-buildup/

RPMFt/LbHPBSFC LBS/HR
4000400.3300.9.392
4500421.6361.2.385
5000459.0437.0.373
5200459.3454.7.381
5400458.0470.9.379
5600454.9485.0.392
5800449.9496.8.396
6000460.1525.7.415
6200454.0535.9.435
6400452.0550.9.438
6600457.7575.2.436
6800446.8578.5.442
7000439.2585.4.457
7100437.7591.7.550
7200431.6591.6.586
7400414.4583.9.552
7500407.1581.4.536