You where writing to Ian;
>     Cause - the 'racer Bob' kid had the vacuum advance plumbed into the
>             manifold port where the brake booster is plugged in.
>             Therefore
>             at idle, the dist had full advance (due to high vacuum) with
>             throttle plates closed, and when the plates opened, vacuum 
>             goes low, and the vac advance retards, causing the timing
>             mark to move back towards initial timing.
 (Mechanical advance is not kicking in soon enough.) 
> 
>     Cure - removed the vacuum advance hose from the brake booster port, 
>            plugged it off, and plugged the vacuum advance hose into the 
>            correct port on the carb that provides vacuum at a varied
>            rate as the engine is revved up.
 This is the only issue which I would add to the experimental list.
Manifold vacuum is/was the source of choice for hot rodding. However, you
do have to couple that with a reasonable amount of vacuum advance (a
10 degree can fr'instance.) Chances are your sons initial distributor had a
20 degree advance can. Wayy too much for any serious tuning efforts that
deviate from stock, especially when going to a hotter cam.  Even in stock
situations its can be too much.  If your get rattling when going to WFOT,
theres probably too much vacuum advance. 
 Heres one to contemplate for the manifold/ported vacuum debate:
Travelling uphill, you open throttle to maintain speed; manifold vaccum
drops, ported increases.  Hooked to manifold you reduce vacuum advance and
consequently reduce the chances for pinging.  Hooked to a ported source, you
might induce a pinging due to the vacuum advance remaining fully advanced.
Not a good situation, and one that could lead you on a path of head
scratching over the cause of the ping.
With ignitions, as with anything else, you have to work the system, and find
what works best for your situation. Basically, all I'm saying is that
Manifold vacuum (except in Chryslers) is not a wrong choice for vacuum
advance.
Alex.
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