Smudge,
The ideal VV dive was vertical from 12,000ft AGL (the steeper the dive, the more accurate the result). It was designed for this purpose: the wings fitted with a 0º angle of incidence so as to reduce the amount of nose-up trim as the aircraft accelerated in the dive. Big and powerful hydraulic air brakes, extending about 9in clear above upper and lower wing surfaces, allowed a smooth airflow over them, so there was little or no buffetting from that source. These brakes restricted Terminal Velocity to around 300mph (knots were not yet in use); we came down with 1/3 throttle open and 2100rpm, partly to ensure that the engine would instantly respond at pull-out and, I suppose, to avoid thermal shock to it.
Our only "bombsight" was a 1in yellow line painted along the mid-point on the top of the nose from engine cowling back to the base of my front panel (this was perfectly adequate). Pull-out was when the altimeter needle passed 3,500ft AGL, we reckoned that would be around 3,000ft true, allowing for lag in the altimeter.
Experience showed that if you pulled with all your strength (most people reached "grey-out" [perhaps 4-5 G]), you'd finish up level at about 1,000ft. This was your "margin for error", but as you were coming down at 400ft plus per second when you began, it left you 2.3 secs to play with - you had to be careful ! Of course, there is no future in flying level over a defended target at 1,000ft, so we eased off on the latter part of the pull-out to get and stay down at tree-top height ASAP until out of harm's way. Your gunner went down "lying on the back of his neck", so as to be able to get on his guns straight away on pull-out (at least, he didn't have to watch the ground coming up on the way down !)
The zero angle of incidence (on the A-31 - VV Mks I-III) made it a fine dive bomber but a very poor aircraft. The USAAC wanted nothing to do with it, but had Vultee turn out the A-35 for them (Mk.IV VV to us) with a 4º AoI (they rejected that, too); which, I suppose, made it a worse dive bomber but possibly a slightly better aircraft. I never even saw an A-35/Mk.IV, but they supplied a number to the RAAF (I don't think it ever dropped a bomb or fired a gun in anger), and to the RAF in UK as target tugs.
The A-35 replaced the A-31's four 0.300 wing guns and the twin 0.300s at the back (we substituted twin 0.303) with 4 or 6 0.50s in front and a single 0.50 behind.
A complicated tale, I must admit. But I don't think that your hurried "Khe-San" arrivals could have been worse than 20º (even 10º on a glide approach is horrific enough) But I know it would feel much worse !
Thanks for the kind wishes, Cheers,
Danny.