Outer Limits 4x4 Board

I have an 1998 model 80 series 4.5ltr 1FZ petrol married to a four speed auto gearbox. Trying to improve my downhill performance I wanted to buy a set of Marks reduction gears, but they are not made for my model. They make a bolt on Crawler Gearbox but with the necessary bodylift and fitting I'm looking at around $6000 which is way too much.

Does anyone else have any ideas?

theres a new product being tested by MQ080 that allows the gearbox to engine brake like a manual gearbox. see the below.

http://www.outerlimits4x4.com/PHP_Modul ... brake+auto