Indeed there are some Japanese parts used in these race tuned engines to improve reliability and performance, the crankcase is usually altered to take twin carbs, Mikuni carbs now instead of Amal, the Ariel crankshaft is still used but machined to take the larger diameter con rod pins for Suzuki or similar con rods that also have needle roller little end bearings, gearboxes are fitted with Nova 6 speed gearboxes, still in production but cost £2000 plus vat and another popular improvement is the fitting of a Newby belt drive clutch... Alloy barrels are used that have steel liners fitted during the machining progress, this opens up the option of a choice of pistons to use as the liners that can be machined appropriately, Suzuki and Honda pistons with a single ring and boost port at rear are popular fittings. Cylinder heads are retained as the basic design is satisfactory usually just receiving a skim.
Going back just over 50 years even Ariel were making changes and improvements to their race tuned engines, in particular 1961 was a busy year for the Development Department, the Despatch Records show a number of Arrows leaving the factory with what they called, Special Engines. Ariel were turning out ported crankcases and barrels, fitting 4 Speed Close Ratio gearboxes, Alpha Racing crankshafts that had Vespa con rods and Dykes pistons. Regards. Jess