<VV> Weird clattering

[Daniel Monasterio]

Guys,
     I have tryed to fix this problem in several ways without success so, I hope somebody could point me on the right direction.
The car is a 67 with a 140 (0.040" overbore), 3872304 cam, 4 speed tranny, 3.27 diff. and 195-70-14 tires.
     Simptoms: While on the road, every time I need to accelerate or maintain speed, on uphill, with the engine running between 2,500-3,000 rpm. it gets a noise like a high frecuency clattering (or pinging ?). Timing is usually at 18º BTDC and works nicely between 1,000-2,000 and 3,500-4,000 rpm., even on hard throtling. On my last trip to sea level, I tried retarding time down to 6º but, it minimized the trouble slightly, only. I have had this problem with 110 heads and 140 heads (0.032" squish quench), with Pertronix II or points while using premium gas (92) all time. Tried with different distributors which worked fine on the Rampy's engine. Tried with and without vacuum advance, no succes. Tried with different springs in the distributor, no success. Distributor is a 0330 with right parts.
     On flat roads there is no major problem if I accelerate gently between the 2,500-3,000 rpm area. 

     What do you think about ? Maybe the camshaft ?

     Thanks in advance for any arrow in the right direction.

     Daniel