More sporting gear ratios

[Lewis]

My car is the HRG 2 Litre, an experimental chassis built in 1948/9 for a Bristol engine (a privateer had previously tried out a pre-war BMW engine
for hill climbing) which went as far as a rolling chassis before HRG realised they were going to be a small player among many others using the Bristol engine for racing. The bits came out to Oz and eventually became a car in about 1995.

The engine is a very early Bristol 400 and I have already sought the views
of this forum about its origin, stamped on the rocker cover as a 75 HP. My problem is the gear box, contemporary with the engine and utterly unsuited to a little car weighing around 600 KGs. First gear takes me out of the garage, second 20 yards further. Third is fine but fourth is really too low, I have had the little car up to an easy 95 mph with plenty more to come if I hadn't run out of road free of cameras and radar - my license usually hangs by a thread.

I need some better, broader, more widely spaced gear ratios. A Toyota Celica five speed box was suggested, but would not fit in the short chassis
and neither would my first hope of a 405 overdrive box.

Any suggestions? What ratios did Bristol 6 cylinders engines use for racing?
Is there available a better set of cogs that will fit my early Bristol gearbox casing?

Best regards,

Lewis Luxton