906 or 915 ?

RustyRatRod said

But don't forget there are two 915 castings. There is also the standard 915 with the smaller exhaust valve. Their ports are not as large too, if I'm not mistaken.

Click to expand...

I think you're thinking of the 516 heads, which are closed-chamber but have smaller exhaust valves and restrictive ports compared the 915s. I can't say I've seen/heard of a 1.60" exhaust 915, but I'm not into big blocks like I once was. If there is, though, I'd assume it's the same situation as LA 915 J heads: The only difference between 340 and 360 casting is the machining. The castings are identical.