From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison table of engine unit weights in pounds for various models.
| Identifier | ExFiles\Box 107\4\ scan0148 | |
| Date | 5th May 1936 guessed | |
| X558 ENGINE UNIT WEIGHTS. LBS. CHINA. PEREGRINE. J.III. 40/50 Engine. 565 417 480 871 Gearbox. 115 110 115 201+ TOTAL. 680 527 595 1072 40/50 Crank 100 lbs. SpectreCodename for Phantom III Crank 70 lbs. † Clutch pit included | ||