Too small. Don't be afraid of more lift and duration. You don't just NEED the extra lift, your motor will want it. Although I think even Thumper prepped GT-40s (no offense to Thumper's work at all) might be too small as well.
I have a similar setup too, BUT had comp custom grind me a "274 equivalent" for 1.7 rockers (and boost friendly )... Since you're at 10:1 C/R (I'm at 8.5:1 too), it will be pretty responsive off idle--I had to bump timing (15^ base) due to low CR and it's still very stout compared to a 302.
The cam will sign off around 6000 rpms on a 331, so the TH intake should be a good match. You'll need to set idle to around 800. It will have a slight lump sound, and a smooth idle if it's set to >=900rpms. I'd keep the Pro-M and get a powerpipe. Having a matched MAF and injectors will be key in tuning (mine idles/cruises like stock, etc...). Also get a pushrod measurer as you should check rod length after install. If you go 1.7 rockers definitely check P/V clearance.
You will like the cam. Your plans should get you over the 300whp goal.
The drop off in the graph looks like the cam. Remember HP is calculated from TQ numbers--was timing being advanced? (looks like SPOUT was out)?
With all that, I was only able to make 263rwhp and 331rwtq. The car drives good. I think the intake and cam are way to small though.
I'll be putting the following on in a couple of weeks and wanted to see if you thought these parts would work much better and get me above the 300rwhp mark:
What heads are you running???
I'm running a smaller cam and twisted wedge heads and I pull 324rwhp and 362 rwtq. I might believe your numbers if you were running stock E7's.
The 263 number was with a really small cam and the TFS Street heat intake. I haven't had it on the dyno since putting the XE274 and Track heat intake on yet.
my hp peaked at a really low rpm and I and some others were thinking it was definately because of the old small cam and intake.