you could ask hawkswood where they get there plugs from, as they build the NP1 solutions for FR2, which uses the same plug. I use the tamiya batteries with the fostex cable, but those cables are really hard to come by now a days. It's a shame because the tamiya battery solution is such a great idea and works really nicely.
For what its worth, there are dozens if DC connectors like that, but they all slighty differ in connector size and voltage so it may be near impossible to know for sure. However, I know some FR2 users who got their units modified with a Hirose connector in order to run NP1s and other such outside power sources.
Check out Petrol bags. I'm not 100% sure if they have one for the FR2 LE, but I'll bet they probably do. Great, well-built modular/customizeable cases. All production sound mixers I know live by them, many sound effects recordists I know use them as well. I use one with my 702. Personally I've had bad experiences with Portabrace and have felt their bags ...
I took own(ed) an FR-2LE and an NTG2. Despite where the pots were, I was always able to get a decent S:N ratio with that combo, specifically using phantom power and not a battery in the NTG (which you are also doing), also with a Tamiya style battery. I'm afraid that I don't recall where the gain pot was, but it was pretty high.
I found the headphone amp ...
Agreed with Mark and Mike on this. Two major gotchas to be aware of, in addition:
The headphone amp is NOY-ZAY. Far noisier than the actual recorded signal. Don't let that throw you.
The CF cards need to be uniquely formatted for either stereo or mono. Super weird but there ya go.