Bodywork / Engine / Gearbox / Transfer box change - info needed

Hi, Little Jim (2007 VVT) has passed the mot with only minor advisories, so decided to throw a little cash at him in the new year and keep for another 2 - 3 years. I am looking at using T Lofley in Mansfield (unless any other recommendations) to do the bodywork (wanting body off and any rust underneath and on chassis sorting out and properly undersealing). Also, going to have the 1.6 conversion done as the 1.3 is just too under powered on the road. Is 2010 M16a the latest I can use without too much work? And finally, do I keep the original gearbox and electric transfer box, or go for the older manual lever transfer setup? If I go for the older gearbox / transfer box, am I right in thinking these are stronger? Also, would this increase or decrease the gearing? I am running 215/75/15 wheels and not really looking to go any bigger. Cheers.

If you change just the transfer case you will have 30% lower gearing.if you change just the gearbox you will have 20% higher gearing.

If you change both you will have 10% lower gearing.

If you change both and the diffs you will have the same gearing.

A friend that has fitted a 1.5 and the earlier gearbox and transfer case, and is running on 215s, said it's a bit buzzy at motorway speeds. In fact he picked up a pair of early manual diffs from me the other day to hopefully remedy it.

I don't do too much motorway, so should be fine. Do we know if there is any noticeable difference between 1.5 and 1.6?