The problem with all this is the rules the DVLA impose on us, for 2 reasons. 1) to ensure vehicles that are put on the road outside the type approval system are safe and 2) to control the recycling of stolen parts.
I don't have the relevant info to hand but IIRC it's quite clear about using a "new" chassis in that you can do it and reusing a second hand chassis which you can't.
Crowblind, does the chassis which you are selling have a chassis number stamped on it? if so your VIN and reg number are tied to it, I appreciate it's very easy to cut out the number and weld in a piece of plate physically removing the ID. When you fitted your new galv chassis whether or not it had a number stamped on it you effectively transferred the number to it. This is where the dilemma arises, legally, you have two chassis with the same ID even if neither has a number stamped on it, It's stupid I know but that is the crux problem and why it can end up in tears if the DVLA get involved. Because the situation where two vehicles have the same ID, no matter how tenuous that connection is, is not allowed one could end up being crushed.
Imagine the situation you have your lovely Land Rover with its nice shiny galvanised chassis, you are driving it round happy as a sand boy. You sell your chassis on and the buyer rebuilds his Land Rover on your old chassis using his original ID.
Then it all turns sour, the guy has his Land Rover stolen and the thief runs over and kills a pedestrian. The police get involved and have the vehicle inspected and they discover it's not got it's original chassis, at this point it doesn't matter whether the chassis has a number on it or not. The plod talk to the guy and being honest tells them that he bought your old chassis, all quite open and above board or so you think. However, the police say is he's driving a ringer and it's got the wrong number/VIN plates because the ID is goes with the chassis not with the bit of plate riveted to the bulkhead. Then what happens then is your lovely Land Rover gets crushed because it has no ID and is running on false plates and the guy you sold the chassis to gets your VIN/reg numbers, loses his numbers as his chassis has been scrapped and everybody gets their collars felt. Unlikely as it may seem but it could and has happened the police (nearly?) always crush ringers.