Timing process questions; timing light questions

[PNW vanwagon]

i've got the exact same van (1989 cargo 73k miles) and the exact same problem: light pinging under load just recently.

i've been swamped with work so i did the same: switched to mid-octane and has 100% fixed problem until i can buy a timing light and adjust timing

it might be a dumb question: but it sounds like you've had trouble finding space to rotate the distributor - were you able to remove the passenger seat and engine cover to gain access to that side of the engine?

i did some research on pinging and a few common reasons:
lean mixture, over advanced timing, carbon deposits in combustion chambers, EGR valve etc

http://www.onestopauto.com/What-causes-spark-knock.html

^ article mentions minor pinging is acceptable - which is the type i have. but i'll still get after adjusting timing as soon as i can. along with an oil change and front brake pad replacement

keep me posted on if you get your's solved - and i'll do the same. i'll be curious to see if slightly retarding timing cures the pinging and allows me to switch back to 87 octane fuel