Hello,
I do not have any personal experience of the ashcroft kit. Have you considered fitting 3.54 diffs from a range rover or 90? it is certainly the cheapest option. I did this to our airportable (lightweight) and it gave me all the extra gearing I needed.
Low ratio was still plenty low, only downside is first gear high range sometimes didnt feel quite low enough - could always drop into low though!
I paid no more than £150 for a pair of 10 spline differentials and I could then cruise at 60mph without an overdrive!
We may be able to help find you the correct differentials if you cant find any for a good price, just let us know.
Kind regards Nathan and Daniel Lloyd
Lloyd Specialist Developments - Engineering Professionals, Automotive Enthusiasts
www.lloydspecialistdevelopments.co.uk