Have you considered the LQ9 ? Since it already has flattops? It might save money , last time I looked the forged pistons were about $600, not sure on the cast.
I have a buddy here with a Tr224 in a 6.0, he doesn't have a stall and it's slow off the line, it will boiling the tires, but it really needs a stall. This is in a 01 ec silvy.
I'll have to pull up the dyno sheets, but somewhere around 335hp to the wheels is what I rememberd, I could be wrong, but I'll have to make it to the shop and pull the data there. That was with completely stock exhaust, you could literally here the engine choke up on the top end, I'm sure he's making more now, he put on some headers and a flowmaster.
I'm trying to talk him into a more aggressive cam and some Stage II heads, that out to put the rear wheel power in the high 300's. The TR 224 is small for a 6L, so if you're looking for a daily driver with a decent idle and good driving, it should work out good for you.
The truck ran a 14.3 with single track, heavy 20's and 3.42's, he still has the 20's but 4.10's and posi, I'm sure it's a bit quicker.
I know you didn't ask, but that is what you can expect from your setup, or very similar. Just wanted to give you an idea of what you truck should do.

So conidering the loss, I'd say it's close enough to 400hp at the crank.

good luck,

allen