Well I might be able to help you out a little. I had a 383 a few years back with dart iron eagle heads (Still using them on current build) and with speed pro flat top pistons the same as you got I had almost 10:1 and my timing was at around 12 initial and 36 total mechanical and 51 with vacuum advance.
I had also a bigger cam then what your using mine was a comp 292h with 244/244 @ 50 and never had a problem with pre ignition with 92 high test. You will not be able to use 87 or 89 you will have problems then. With that cam and the big amount of overlap and duration it will be borderline but you will probably be able to pull it off but I can not say 100 percent.
Make sure its not burning too lean or rich and find just the right spot. The thumpr cams do make good power and torque don't let anybody fool you but some of the other grinds like the comp xtreme energy line will give you a little bit more but is your just wanting something to run good and sound good they are fine. I have a big mutha thumpr in my 350 roller build up.
I wish I went with the mutha thumpr instead. The big mutha thumpr has been nothing but a big mutha problem tuning wise. Well good luck with your build it will make at least 400 hp or more. It will sound good