Below is a full list of the basic modifications Ken made to the standard MGB in order to create the first Costello MGB V8 in 1970. Most of these changes were later replicated in one way or another by British Leyland. They are listed by area. Optional Costello modifications are shown in italics and, since they were available at the time the cars were built, if carried out retrospectively, in mgcostello.com's view would not compromise the originality of the vehicle.
The rear bulkhead and inner front wings were re-profiled to clear the Rover V8 and its specially fabricated tubular exhaust manifolds. Bespoke cast alloy engine mounts.
Modified (by Triumph suppliers Torrington) to have two knuckles (universal joints) with the addition of an extra universal joint, also for clearance.
Buick/Oldsmobile/Rover P6 215 cubic inch V8 in 155bhp tune. Without extra modifications, the available engine configuration at the time necessitated a rather distinctive installation, with a remote centrally-mounted radiator expansion tank and the top hose passing underneath the fan belt. On some blocks, the projection on which the engine number was stamped had to be machined to clear the exhaust manifolds.
Optional modifications were ported and polished cylinder heads, a 'fast road' camshaft and Lumenition contactless ignition.
(In Mk III  specification, a capacity of 3.9 or 4.2 litres was available, together with a standard-fit Costello injection plenum, a K&N air filter, an enlarged throttle body for the larger engine, and a re-mapped ECU).
Reshaped to clear front cross-member. A cast alloy option was available later.
The radiator was enlarged in capacity and moved forward, the ducting panel redesigned with oil cooler installed beneath and a remote oil filter fitted on the right inner front wing. An electric, thermostatically controlled fan was used in place of the belt-driven original.
Mk I cars used the standard Rover P6 configuration inlet manifolds. For the Mk II, this arrangement was superseded by a Costello cast alloy manifold to take two SU HIF-6 carburettors or one rearward-facing 40 DCOE Weber. A Carter/Edelbrock (now Weber 500cfm) carburettor on a matching cast alloy manifold was optional - and was actually standard on a few Buick-engined cars.
Fabricated tubular 'block hugger' manifolds by Mike the Pipe, modified big bore MGB exhaust pipes and silencers.
Bespoke glass fibre with shaped bulge to clear P6 configuration SU carburettors. Later, Mk II cars did away with the bulge after the introduction of new, lower-profile inlet manifolds.
Adapted bell housing, uprated clutch, standard gearbox modified to lock out overdrive in third gear, 3.07:1 final drive ratio (MGC). The Costello five-speed gearbox became optional on later Mk II cars.
Uprated front anti-roll bar. Uprated lever arm dampers optional. (For Mk III cars, the Costello cast alloy front suspension conversion with tubular dampers had become available).
Anti-tramp bars, Panhard rod, uprated lever arm or telescopic dampers optional.
Fitted with high performance Ferodo DS11 pads. A servo was fitted as standard, if not already present. Some later Mk II cars were equipped with optional four-piston Austin Princess or Rover SD1 calipers.
Wheels & Tyres
Standard fit Dunlop 14 x 5J alloys with 165 or 175/70HR x 14 tyres. Cars originally equipped with wire wheels invariably had stronger, Minilite pattern centre-lock wheels fitted instead. 185/60 profile HR rated tyres were a later option, as were 15" wheels (Necessary for clearance with SD1 calipers, depending on the dimensions of the wheels originally fitted).
Glass fibre bonnet (as above) on the first 50 cars, bespoke aluminium 'eggbox' radiator grille, Costello V8 badge on the rear panel.