Galvanising gives off poisonous fumes when welding so make sure you are well ventilated.
As always you really need to get back to bare metal for a sound weld so you are going to have to mess up the galvo around where the mounts go.
I'm not sure how different the mounts are between the TD5 and Puma but if possible I'd be looking at making up modified mounts to bolt to what you have rather than chopping and welding the chassis.