It sounds like you bought the Large engine mount with the high post, that it used for when your using an adjustable diff. See that Large engine mount that you have is alittle higher in the back where the diff case mounts, because when you use the adjustable diff, that diff needs diff risers because of the lip that the diff has. I have some diff risers here that I'm not using that I can sell to you. Another thing your layshaft will come out, it is alittle hard because you have a brand new bearing in there that grabs the layshaft when you slide it in. Spay a little bit of WD40 on the bearing and layshaft and it should come right out, because they all do that.
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THERES NO SUCH THING AS TOO FAST!