Thanks for the info.
I have used a Rover header tank on my car.
It is positioned on the LH turret and is plumbed into the bottom hose.
The position is fine (the coolant level corresponds with the top of the thermostat cover)
however I see the Roy (Triple Tango) has managed to use a VW tank positioned so that its minimum level
is above the thermostat cover, this extra height being worthwhile. (A VW tank also has a level sensor.)
I may experiment repositioning the Rover tank a la Roy's solution. To be honest, the position I used was in
no small part influenced by the length of the 16mm outlet hose (one metre)
.
It is easy enough to remove the tank and swing it out of the way to allow access to the engine, without having to
drain the coolant.
The bodywork issues on your Sprint look fairly minor.
I have never been a fan of that black underseal, having many times had a sinking feeling when spotting some that
has sagged. On my car I have used clear Waxoyl for the exposed (visible) bodywork.
For the internal sections I used the Bilt Hamber stuff.