That book is great, I've got it myself.
The vn box won't bolt up, I'm half way through that conversion my self. You need to find a v8 trimatic, assuming its trimatic pattern, make sure the linkage is on the correct side. if you take it easy the banjo will cope, but if your going to give it a bit of stick, you'll find it won't last long, but it'll give you time to sort a new diff.
If you really wanted a t700 box, it either get the block drilled or conversion kit. Adaptor, tailshaft, box mount, adaptor plate or redrill, adaptor ring on the converter if using an adaptor and modify the torque converter, then you need to sort out speedo cable, kickdown cable and then the torque converter lock up!
A lot of work for an extra gear. I'm going it only because it was cheaper than building a new trimatic.
I'm not sure what can I have, but it's a reasonable one. I've heard I think it's a crane, tq20 cam, if you look it up on they're website it'll give you the rundown on specs to compare on other brands.
It'll be a good experience to build a 253, they're pretty simple, all your bolt torque specs are on page 77 (I think) in that book. Just have a check at all the bearings while the engines out, and do the rear main while it's out too, saves having to do it later doesn't the track
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