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When it comes to engine blocks, there are two distinctly different 4.6 iron passenger-car casts and about 10 different cast numbers, even though they are mostly identical in construction. The first iron blocks (1991-92) have cast No. F1AE and have solid dowel pins for the transmission, and the first four main caps are cross-bolted with "jackscrews" between the block and the main caps, but the rear main has no cross bolts. This block was used in 1991-92, and all parts will interchange with new blocks, but the F1AE block is not the best choice for performance applications. The block shown in the photo is a later 1999-up 5.4 Lightning block with cross-bolts on all the mains.