There's no such a thing as a "sleeve" in M62 block - these are made of alusil which is a material and not a coating like nikasil - you can rebore the 4.4 block just by 1 mm to get the 93 mm 4.6 bore. The only thing being neccessary is a lapping of cylinder walls with special "brush" to disclose the Si-crystals in the Al-matrix, which are holding the oil particles for better lubrication.

Actually the only difference between Alpina 4.6 block and BMWs 4.6 block is that the Alpina used the 4.4 blocks and BMW used different casting form for 93 mm bore of 4.6 l block.

The block height of 3.0 L M60, 3.5 M62, 4.0 M60, 4.4 L M62, 4.6 M60 and M62, 4.8 M62 and 4.9 S62 are the same!

So - just go on!