Complex sentence: Those TR7 Sprints that are known were fitted with the 5-speed gearbox mated to the 3.89:1 rear axle that was standard on the 5-speed TR7s and the alloy wheels that were optional for later TR7s and standard on Solihul built fixed-heads.
Split into simpler sentences: Those TR7 Sprints that are known were fitted with the 5-speed gearbox mated to the 3.89:1 rear axle that was standard on the 5-speed TR7s. The pre-production cars had the alloy wheels that were optional for later TR7s and standard on Solihul built fixed-heads.