Señor Murdered, forged internals in a stock block will not make a lick of difference really. The factory 5.0 block will be the weak point wether you split the valley or the caps start to walk. The old pushrod 5.0 motors had decent internals.
A factory 351 will handle 600 hp all day if built correct.
2016 VW GTI 2.0 Turbo
1989 Sonic Blue LX Coupe, 349 ci, TW heads, TFS Track Heat Intake, 75mm Accufab TB, 80mm ProM, 30 lb. inj, TKO, 3.73, 31 spline w/ TruTrac, MAC 1-5/8" LT headers w/ H pipe, Flowmaster, electric fan Moates QH
391 rwhp & 424 rwtq...Mustang Dyno 11.5@122mph