I currently have a 392 that was originally rated at 430HP. I got tired of it pretty quick and then put some different heads on it. Last time I checked it was making about 410-425 RWHP depending on the dyno.
I am now like you, looking at doing a repower this winter. I think this time I am going to shoot for 600HP with a 427W or 438W Dart Block engine. I think if you are going to do it, then put something big in there. Cheaper now than later.
I have not contacted anyone yet, but I have been looking at Keith Craft and also following Brent Lykins (B2 Motorsports) engine build posts a lot lately
.