I am starting to build my 406 tomorrow and needed some help. Here is specs on it:
400 sbc 2 bolt main bored .030
bowtie heads 034 casting (2.02/1.6 valves)
stock 400 crank (3.75)
lunati bm II cam .480/.480
standard volume mellings pump
arp everything
edelbrock rpm air gap intake
quick fuel modified 4777 holley (650 cfm)
stock reconned' 400 sbc rods (5.565)
Speed pro 10.14 pistons (with 64 cc heads)

my question is I have a carter m6900 mech street pump would this be a good choice to run on this motor? or could I use the original fuel setup? Car is an 87 Iroc-z Convertible that had the lg4. I think I should run the m6900 but I was reading and saw carter also makes a return style mech pump. Would the electric in tank booster pump work without the ecm in the car anymore? if I just run the m6900 will my fuel gauge work correctly or will I need to find a pickup from an older car if so any recommendations on what kind of vehicle I should look for one from? Also I am using a stock 700r4 and torque converter for the time being will this hold up? Not really sure what my rear end gears are as I haven't even check yet. any idea on what most common was for the lg4?

 

In my opinion, an electric pusher pump at the tank with a mechanical at the engine, with a return system of some sort, is the way to go. The return-style mechanical pump looks good to me, but I haven't actually run it yet.

If you don't run the in-tank, take it out. That has been discussed often. It won't affect the fuel gage operation. You should be able to wire the in-tank to operate properly, although I don't know whether it is tied to the ECM or not (my guess would be not).

A properly prepared TH700 will hold up to the kind of power you'll be making. A stock one won't last long if you use the power available. Take it easy, no problem.

Most common gears for LG4 were 2.73.