Many photo etched metal, cast or turned metal and cast resin engine detail items are available for 1/24 - 1/25 bi-scale applications from aftermarket companies like S&S Specialties, The Model Car Garage, R&D Unique, Detail Master, Parts by Parts, Replicas and Miniatures of Maryland, MAS, Scale Repro's Plus, Altered States, Performance Detail Products, Scale Auto Details, Studio 27, Sakatsu, Acu-Stion, Modeler's. etc.
Scratch Building Supplies: Many engine details like wire looms, dip stick tubes, accessory brackets, bolt heads, washers, etc. can be scratch built from metal sheet, plastic sheet and strip, tubing and wire. K&B offers metal sheet, rod and tubing. Evergreen offers plastic sheet, strip, rod and tubing. Hypodermic needles can be used to make dipstick tubes for engines and automatic transmissions. Radio Shack is a source of wire of all sized for engine bay wiring (alternator, ignition, etc.), spark plug leads, spark plug boots, radiator hoses, heater hoses, vacuum hoses, PCV hoses, seals on dip sticks, etc.
Metallic Engine Components: Testors Metalizer paints can be used to give a realistic finish to the metallic components on an engine (intake manifold, exhaust headers, alternator, carburetor, water pump, etc.), by using several different shades like aluminum, magnesium, burnt steel, steel, stainless steel, brass, etc. Transparent blue (Candy Blue) can be used to represent heat discoloration on exhaust headers when dry brushed over aluminum or stainless steel. Mix aluminum and brass metalizers 1:1 for a very nice representation of the gold colored zinc-cadmium plating on carburetors and brake master cylinders.
Throttle Return Spring: Strip the insulation from a length of fine wire about two inches long. Tightly wrap the wire around a #70 drill bit about ten times and squeeze the coils together as you wrap. Remove the coiled wire from the drill bit and bend the ends 90 degrees to the coil and straighten them out. About 1/16" from the coil, bend the wire 90 degrees to make loops to attach one end of the sprint to the carburetor linkage and the other end to a bracket on the manifold. A touch of Super (CA) glue or clear gloss paint will fasten the spring to the bracket and the carburetor linkage.
Throttle Linkage: Strip insulation from a piece of fine wire about one inch long. Roll the wire under a metal ruler to straighten it. Bend one end 90 degrees and insert it into the carburetor linkage and the other end through the firewall. A touch of CA glue or clear gloss will fasten the linkage to the throttle on the carburetor. A short piece of wire insulation can be used to represent a rubber grommet where the throttle linkage passes through the firewall.
Spark Plug Leads and Boots: Strip the appropriate color insulation off of a one-inch length of larger wire for the plug boots and distributor cap boots. Slice the insulation into pieces about 1/32" long for individual wire boots. Cut 1.5" long lengths of finer wire of the appropriate color for the plug leads and thread one boot onto each of them. Drill holes into the heads and distributor cap with a #70 drill bit. Attach all of the plug leads to either the distributor cap or the heads using CA glue or Five Minute Epoxy. Make spark plug wire looms by drilling plastic strip, metal strip, or use photoetch parts. Thread the plug leads through the looms and cut wires to size. Place another boot on the opposite end and glue the wire with CA glue or epoxy to the engine. Correct engine firing orders can be found in repair manuals.