Changing the top end on my 1999 454 MPI mag to intake and carb. What all will I need to do this? My concerns are wiring harness, fuel pump, currently has the cool fuel system on it, and if current throttle cable will work. I have a thunderbolt IV ignition off another boat I plan on running. I'm sure there are things that I am not thinking of.

Its a easy swap, the EFI harness is stand alone, as far as merc dist is concerned not sure but a early one would work for sure, I usually run a H/P HEI on these and works well. you will have to set up a low pressure fuel pump as you only need 6-7psi, I used elec in the past as I dont care for the mechanical pump run from water pump.

Wrong questions on part - Sorry about that one, deleted them

The Holley Sniper efi kit is almost as easy as a carb swap. Might be something to consider.