If the goals max mileage with few maintenance related failure issues, if the goal is max durability and power is not the only or even the main consideration, you make choices based on increased durability, a few factors in the component design do increase durability and the use of better quality aftermarket components will add considerably to the engines life span. stress and heat must be minimized ,controlled and consistent, and lubrication maximized, and Id suggest a multi spark ignition, and Id use a multi coil coil on plug ignition, and limiting the rpms to about 5700-5800 rpm and keep the compression down near 10:1 so you could use pump octane gas. Id like to use an over drive transmission, a 2500 stall converter and a 3.54:1 rear gear. Id use stainless 1,3/4" full length headers and a full 3" dual exhaust with an (X) pipe. Id use bosch platinum spark plugs Id suggest due to what Ive seen over decades that almost all OEM parts are built to be the lower price bidder components, and as such Id damn sure use aftermarket parts in most areas thus they are not nearly as strong or durable as the better aftermarket clones, Id specify clevite H bearings and I use a standard capacity standard pressure BBC oil pump, if I was building a SBC engine to make reasonably good power but with long term durability as the main goal, Id select a forged two piece rear piece DART block, https://www.summitracing.com/parts/drt-31161111#overview https://www.summitracing.com/parts/sca-1-40570#overview use 6" rods with 7/16" ARP rod bolts and a 3.5" forged crank with forged pistons, https://www.summitracing.com/parts/sca-1-40570#overview Id select a hydraulic roller cam with a bit less than .520 lift and about 215-220 duration at .050 lift on a billet cam core, Id install steel roller rockers with a 1.5:1 ratio, https://www.chevydiy.com/wp-content/uploads/2017/01/17-6.jpg https://www.hardin-marine.com/p-100245-sb-chevy-valve-spring-oiling-system.aspx Id use a 7-8 quart oil pan http://www.grumpysperformance.com/wpan3.jpg and wix extra long oil filters, and a few ceramic high temp magnets to trap metallic debris http://www.grumpysperformance.com/51800.jpg and change oil every 5K miles and use a mix of 6 quarts of mobile 1 synthetic 10w30 and a quart of MMO, id use direct port injection with 22 lb injectors my goal would be something like a 350hp/380 ft lbs power band, Id use heads with bronze valve guides and hardened steel valve seats, with about a 190cc-200cc , port size probably brodix IK heads Id select the (FIRST tuned port INTAKE) https://firstfuelinjection.com/ keep in mind direct port injection limits wasted fuel and allowing fuel to wash lube from bore walls rings etc. Id specify use of an oil cooler and a larger than average radiator with at least a 60% antifreeze mix that gets changed every year.