I would start with the complete 4.6 short block...There is not a difference in quality between the 4.0L and 4.6L... The castings equally suck and if anything, the 4.6 is more prone to sleeves failing due to the thin walls to accomodate that were not much of an issue for the smaller bore 4.0L...4.6 also had porousity issues and lest we forget, the famous oil pump housing alignment dowel pin that thousands were not set into the block/aligned correctly and they subsequently machined themselves to catastrophic failure. As the castings went on, they got dirtier and dirtier and with the 4.6 being near the end of the line for this block, they are some of the worse, hence the high failure rate of head gaskets and liners. The casting quality is so bad LR nearly gave away all of their extra stock as no one wanted to buy them. History if this whole issue can be found from Cosworth who is recasting the 4.0L/4.6L blocks. These are the ones you want. I would, however, for the price, throw in a 4.6 GEMS engine from a P38 complete if it had good compression and around 100k as it should have had it's teething issues sorted by then...hopefully... I have several 4.0L and a 4.6L not bashing, 4.6L pulls very well, but it is not without it's own issues. Just wondering thoughts on using it in the D1... I am sure it has been done.