Okay, I did some digging. Found one of many of ArcticFriend's posts. Here is table on a 502MPIMAG 415hp:(should be quite similar to 454MAG MPI 385HP)
Note: do more diffing under his name and you'll surely find more :

https://www.offshoreonly.com/forums/...pi-timing.html

Now that you're on TDC :D also run the firing order on the plug wires from the cap to the plug may have 2 flipped.....

it’s a 1999 7.4 mpi 310hp version. The serial number has faded off of the plastic shroud on the top so i don’t have that unless it’s stamped on the block somewhere

i triple checked this when i put the new cap, rotor, plugs and wires but I’ll check again tonight!!!!

Being 310HP you have the L29 which has 2 knock sensors
Have you tried to remove or disconnected the sensors or knock module to see if timing increases?

I haven't but I will try that this weekend and check timing again. If it's the same, what else could be causing it not to advance?

That's what doesn't make sense. The L29 should have a MEFI 2 ECM. If the knock module is what is keeping it from advancing then there should be a code 43. Have not read where codes are found. Now if the ECM test on first throttle up the knock module to see if it can make it knock. If this doesn't happen (mine did that after repower) then there would be a code 44. So no codes but no advance. As said previous, the EST module and ECM is what controls the advance.

If there was a code 42 then it would be the module is not coming out of bypass

Again no codes so it doesn't make sense, so I'm spit balling

I scanned it and it pulled a code 44... no knock detected. What is the procedure to diagnose this code? thanks, I think we're getting closer!

also, I've been running premium ( i think its 93) octane fuel. From what I've read, these older engines were designed to run on 89 and that the higher octane fuel could cause code 44? Not sure what I take of that....?? Thoughts? I figured higher octane would be better

No you do not have that problem. The specific issue you are referring to was for a small batch of 454/502 Mag EFI/MP motors around 1994-1995. There was a Merc service bulletin put out at the time addressing the issue. Basically during engine start the ECM would advance timing until knock was detected which verified the knock sensor was working. If it didn't detect knock it would trigger a code and retard timing. This does not apply to your engine.