another issue you will hit is the front crossmemeber. the mk1 engine bay/front end is short by a couple of inches than the mk2, so when you fit the mk1 scuttle, wings bonnet and front panel, the front crossmemeber will be sitting proud of it all, further forward.

it might be just as much work to 'spaceframe' the front end. perhaps weld in a rollcage and then build off of that. just a thought.