I got a 89 squarebody 454/400 trans, and I desperatley want an overdrive. I found one from an 88 half ton 2wd. Will this work in mine that has the big block? Or is there a particular O/D trans that I need to be looking for.

700R4 really isn't strong enough in stock form to put behind a big block. They can be built strong, but it's really not the transmission for the job. However it may be the easiest overdrive for you to adapt. Is your 454 still running the throttle body? You'll probably need to change the throttle cable bracket, though it's likely to require some hacking to make one, plus add the stud to the throttle bracket on the TBI to hook the cable up for the 700R4. That's not a "kickdown" cable like some people think, it's called the throttle valve (TV) cable and it must be hooked up and adjusted properly for the trans to shift right and regulate its internal pressure, if it's let off or adjusted loose you will roast the transmission in a hurry. You'll also need to wire up the lockup function of the converter (4 pin connector on the side of the trans) and there's a couple ways to do that, either with a switch you control, or I think there's an aftermarket vacuum operated switch.

The strong overdrive trans to put behind that big block is the 4L80E but they cost more, and require a computer to run 'em, unless you convert it to a full manual valve body. However, you could probably score the parts from a boneyard big block truck - 91 through 94 - and get everything. Trans, computer, harness.

Richard