Check the start of this thread. Your question was answered a week ago.

Here's an idea. Call up a transmission shop, and ask them if they would
be willing to do something like this. Depending on how busy/crazy they
are, they might say yes, but will probably say no. Then ask how much it
would cost to do it if it were possible, and if they'd guarantee the
work. Take the absurd figure they give you, and compare that to the
cost of a manual 90-91 integra on a used car lot. Then take the figure
they gave you, and if you still want to go ahead with this, add on the
prices of the tools you'll need, and alternative transportation while
you try to sort out the inevitable problems you run into trying to jury
rig this thing, etc. And there'll be no guarantee it'll work in the
end. 90-91 integras typically sell for about 2500$ US these days, plus
or minus a bit for condition. That's not a lot - is this project worth
it? If it's a hobby type project, and it's not your regular ride, then
why not? Just go for it. But if this is your main car, and you just
want a manual because you made a bad choice when you got the thing,
then I'd say suck it up and move on. Live with the automatic until you
can afford a car with a manual.