The 1.72:1 roller rockers will necessitate the removal of the rail running on the inside top of the valve covers, otherwise you'll run into clearance problems. I'm not sure what pushrods the 1.72:1 RR use, that may be something you'll also have to replace.
Why are you suprised to see 6000rpms? The stock 5.0 redlines at 5900 not because of the engines reliability factor at higher rpms, more because it's not designed to make power beyond that.
The stock hydraulic lifters begin pumping up as the r's really climb, but they should do fine till fuel cutoff at 6250rpms without a whole lot of difficulty. I wouldn't be scared to send the stock rotating assembly to 7000rpm. Just not with those lifters. What would it matter anyway, you're not making power up there at all.
It's not like switching to 1.72:1 RR will be making good power at 6k anyway. You are limited by heads, and exhaust, along with intake.
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