Editing AMC V8 engine (section)

=== "Service replacement" blocks ===
There was also a "Service Replacement" block made as a modified GEN-3 design. This is a 401 casting (same casting number) without the displacement cast into the side and with a 360 bore and thicker deck. In theory, this single block could be built as any 343-401 GEN-2 or GEN-3 engine. A dealer could stock one or two blocks to use for warranty replacement.

The main bearing web area was thicker in the 390, 401, and SR blocks, thick enough that two additional bearing cap bolt holes could be drilled and tapped for an aftermarket four-bolt main cap, providing a stronger bottom end. AMC never built a factory four-bolt main block, they sold aftermarket four-bolt main caps through their Group 19 performance parts program.

The SR block was also sold as a heavy-duty racing block. It appeared in 1970 in time for the 1971 Trans-Am racing season and was used in the factory Trans-Am backed cars prepared by TRACO for Penske Racing, with Mark Donohue the primary driver. Since it was a standard factory part it did not have to be homologated under T/A rules, and ''was not'' used in the 2501 "Mark Donohue" [[AMC Javelin|Javelins]] built to homologate the "ducktail" spoiler. Those received standard 360 or 390 engines, buyers' choice.