If you are still "on the cheap" theme you probably could install or possibly mod your vacuum can on the dizzy to retard timing when in boost.
Need to read up on them. IIRC my friend says he can mod a stock type canister to give you boost retard?
He is a Corvair expert & has access to the factory GM vacuum cans that retards the timing while in boost.
He has tried several brand new NOS ones, used ones etc, on back to back tests & the amount of timing retard is all over the place. not consistant @ all.
This way you could run more initial timing = better mileage, better turbo spool up, etc. Something like this but for your HEI. http://www.dalemfg.com/dale_018.htm
Personally,, I would just save up for a MSD BTM. If you are going to save up for any new mod, get a timing control devise first, intercooler set-up, methanol injection.
Are you running 92 octane now or just 87 octane?
I am wondering why you ask, (after the fact) if you can run 15 psi boost pressure on your stock engine after you had already done 12 or more WOT blasts.
You already done so,,,, not safely mind you.
I am really shocked your engine stayed together this long, w/you running 15 psi, A/F ratios being really lean, way too much total timing, running 88-89 octane (not even 92 octane) listening for detonation w/no downpipe connected to the turbo & no exhaust system.
I have to say, you are probably one of the luckyiest guys I heard of just slapping the turbo on, no wide band on (initailly), way too much timing & running cheap gas, no intercooler etc.
I am just saying, you are really lucky.
Glad you did not blow it up,, you are not done by a long shot, just take your time & tune it, tune it, tune it!
Snowman, BTW, how about some more pics of your downpipe & pipeing to the carb, bov, etc.
