LIC Motorsports Adj. Timing Belt Idler Bearing Set (EJ)
These parts are designed for long blocks that have been narrowed down from resurfacing the heads during a rebuild or decking the block and/or both. When that process is done it effectively retards the timing, this is because the belt has not changed length and something needs to make up that difference in the slack (the tensioner can only do so much), and likewise if you have different thickness head gaskets, these are perfect in conjunction with that, as the same issue is present (just vice versa, which is a lengthened block).
This is what the LIC Motorsports adjustable timing idlers were designed for and is only recommended to bring your cams back into proper alignment.