Darton MID are very good as they use the x3 O rings seals on the bottom of the sleeve as apposed to most others sleeves manufactures using sealant (from application I know). It's all in the machining process, I know of open deck Honda engines running 1500 bhp requiring approximately 50+ psi of boost to achieve this so the sleeves have the pedigree.
If you plan ahead and source the parts then somewhere between 6-8 weeks is realistic, many of the parts to take to 5.7L are built to order which can delay things significantly.