Warnings can only be helpful before someone makes a mistake, kinda of rubs it in after they already spent the money.
The cam is fairly nice size for a flat tappet, in a 390 it would be kinda big, as motor size increases, 427,428, 454, 468, 482,and so on, the cam gets smaller. Would it run in a 390, yes but it would be lacking torque on the bottom end. Would I run it in a 390 if that was all I had, hell yes.
I may throw the Crower cam in my 390 and run it till the 468 is done. Eng spec's I posted earlier are backwards it's 4.250" bore x 4.125 Forged Scat crank, for the 468 with Crower rods. I'll be running a 3,000 stall and 3:50 gears on the street. If your one of 25 who bought this cam, the bigger the motor the better off you'll be, but if you don't, run it anyways or put it on the shelf and shelf race it... 
Here are the cam cards for both cams. And both cams have identical 99 deg's of overlap. The Crower has 4' advanced ground in on 108 LSA and the D cam has 5' of advance ground in on 107 LSA. And the D cam has .015" smaller base circle than the Crower cam. And the D cams 614" lift is calculated from the Hydraulic 1.73 ratio x .355 = 614 - .025 = .589" lift, with Solid rockers: .355 x 1.76 = .6248' - .025 lash = .5998" rounded to .600" lift. And the exh timing are identical on both cams, both open @ 68 and closes @ 24
Well, we're kinda in bad shape if we do warn, and bad shape if we don't. I kinda felt bad even asking Greg about running it in the other thread. But it would have been a mistake and I hated to see him make it.
The thread on the other forum clearly had a description of the intent of making those camshafts, as well as a clear description of the specs. If someone bought a camshaft that has 273° of duration at .050" lift, then I have to assume that they bought it while seeing those specs.
That Crower camshaft would be closer, but to be honest, I don't think either one of them are anywhere close to what you need for something going down the road with a 3.50 gear.
I understand that a lot of guys want sound from a camshaft. For crying out loud, that's why Comp went and made the Thumpr line of camshafts. You wouldn't believe the number of guys who call me wanting a custom and they always throw in the line at the end, "Will this have a little bit of lope to it?" I get it. I like big cams as much as the next guy, and if you'll notice, all the engines I build for myself are pretty high stringers.
I will say this though, I built the 390 dyno mule, which peaked at 7000 and pulled to 7500 with a hydraulic roller. It had 90° of overlap and the next iteration camshaft that I had for it before I sold it to Shady, was something with less overlap. Not because I didn't like the sound, but because I thought it would make more power with less. That's pretty common.
So, at the end of all of this, I think you're making a mistake too, Richard. I think both cams are incorrect for your application. If you're in it just for the sound, that's all fine and dandy as long as you say that up front. However, if you're building something to run, and I'd say you are with Blair's heads and a well-ported intake, I certainly would either reach for another cam, or throw a deep gear in that car. That's a very mismatched combo. With a 3.50 gear and a heavy car, I'd be somewhere around the high 230's/low 240's, for .050" duration. Remember, that there's a byproduct to all of that overlap: inefficiency at low rpm. I get it, that's what higher stall torque converters are for, but a 3000 rpm stall isn't a lot for something like this.
Let me also make the general point that it probably won't be the case with those Pro Port heads, but you can't keep throwing duration at an engine, expecting it to make more and more horsepower. There's a very distinct line, where the power starts falling off. When that happens, you end up with an engine with an extremely small powerband, with no guts down low, and no butt up high.
