Question about a 20R motor's tranny

[IXIswamperIXI]

A friend of mine has a 3 speed automatic behind his 20R motor we are wondering if we can lower the gears internally or is there a 5 speed with a lower first gear?  Also maybe specs on the 3 speed he has (ie: ratio of 1st gear) so we know what to look for in other trannys.  Its for a buggy, he paid a lot for a 4:1 drop box but it wasn't enough. 

Thanks,
Swamper