Shortening chassis

Hi,

I have a 1991 range rover chassis I want to shorten to fit a series body 88" on for a off roader ( not for road use before any one asks)

What is the best/ easiest way to do this? Do I just remove 12" from chassis rails - straight bit, Is it ok to do straight verticle cuts and then plate over each side with 4mm plate, or should I cut it in a diagonal?

Thanks

diagonal welds in thin material are pointless ,you are just making the haz larger.
Sleeve inside and plugweld through then plate on the outside.The internal sleeves with plug welds help hold allignment