It's not a factory 400, it was a 318. However, it was converted using all factory stuff.
I'm going to put an OD trans in it, no doubt in my mind. I have an an aluminum case 833 od on the shelf that needs to be gone through. From what I've read, it will need to have a case bushing installed. No biggie if it's apart.
The tough part is finding the #670 bell housing that fit big blocks and have the dual bolt pattern for the NP435/833. They are around but pricey.
I would like to be able to use first, it's a better gear split than just the three speeds. It would help coming off idle. Passon makes a 5 speed cluster gear with od I could put in. I might do that. The truck has a 3.23 gear so highway cruise rpm is not too bad but a little more gear would be good for the overall combo, maybe a 3.55.