I stand corrected on the x member,however i stand firm on the other points.As they say"the proof of the pudding is in the eating" and i have eaten a few.
I still think the H165 will handle the turbo,remember half the ute's with CA turbos still use this diff.
Another option would be the 120y borg warner,although i have no first hand experiance i'm told they are as strong as an ox but you have a width problem to be corrected.
Personally i'd sell the 5 speed for about a grand(if you need the money)and fit a Toyota box.

re. diff.. I don't want to blow up the original ute diff and then it be impossible to find another whereas 120y diffs are everywhere.
I think the 5 speed i have is a 60? Is there such a thing, i could go check but cold out and cbf'd. if so your saying this box will not handle the extra power..saying that i'm generally fairly rough on g/boxes so a T50 would prob be the smarter option?

will a 5 speed handle the power of an A14 turbo?

Yes, the B210 A14 5-speed 63-series.

-Is there a off the shelf gearbox Xmember to fit a 5 speed to a 1200 ute?

Yes, the 1200 automatic xmember.

-Will the shifter come through the floor in the same place?

Yes. All a-series gearboxes come out in the stock shifter hole.

A few quick answers
1 A series box NO
2 NO
3 A series YES
4 NO,but why would you change it anyway as the H165 is stronger than the H 150 found in the 120y
5 Not an answer to anything but why don't people put thier location when joining the site anymore?

The original diff is stronger or as strong, and you probly want to look for a a63 5 speed or a dellow/toyota 5 speed kit both are upwards of $1200

A few quick questions, will a 5 speed handle the power of an A14 turbo?
-Is there a off the shelf gearbox Xmember to fit a 5 speed to a 1200 ute?
-Will the shifter come through the floor in the same place?
-Will a 120y diff fit a 1200 ute(don't want to break the original) and handle a locker?