you wont find a 6spd (aka T56) to suit a E series,
theres a EF/L XR8 going around in Perth with a T56 ... clampy owns it still?
he got a custom bellhousing and internals or something so it would fit.
if you are after a stronger manual box, then you cant go past the (5spd) TKO600

about $3500 .. but almost indestructible

you will get a T56 standard for around $4k ... and thats not to suit E series