Randy,
I think the guy has you confused and may be himself. Ford is different then a GM car in that the Ford has had an external solenoid mounted "elsewhere" since, well, about as long as they have had electric starters. The GM's have their solenoid mounted on the starter itself. This solenoid, either Ford or GM, works as a really heavy duty relay, one that can handle an intermittant 500 - 1000 amps current draw or whatever is needed to start a particular engine.

Simple explanation. Picture a starter solenoid. There are usually 3 (or 4) wires. Low current (your 1 or 2 small ignition wire circuit) makes a primary, for no better term, circuit by pulling an iron armature up to the high current side of the circuit (the starting or secondary, circuit) which is connected through the solenoid case by the large capacity wires. They are separate circuits and systems - and as a matter of fact, the energized starter circuit is basically a straight line line directly from the energy source (the battery) where the light duty side is the ignition/running side of the ignition switch . They are not electrically connected - ever.

My advice to you is to have this guy give you a schematic and a full description of the operating principles as, quite frankly, I don't believe he is, IMO, going to improve on Ford's 75+/- year old tried and proven system. I assume that you will mount the battery under the floor or in the trunk - the solenoid can go there as well. You just have to run one or 2 wire gauge size larger wire to the starter and longer wires from the ignition switch as well. It doesn't need to be on the fire wall - it just needs some weather protection (in CA - yeah, right!!).

Hopefully this is not confusing - just be very wary of someone that say he can eliminate this solenoid - a Ford starter just wont work that way and running it directly from the ignition switch to the starter wont cause any problems either - it will just instantly self destruct