I know tmz06003 is on a sabbatical at present, but I think one of his 55s is going to make the best DP1. It would however, need the headlight added for it to be a true representation. The built-in ones lack the detail to be a truly acceptable asset for today's standard.
As I said though, the dimensions of the production shell isn't right for DP1, DP1 was a little taller and the nose shape is slightly different (iirc, the cab windows are more raked on DP1). Basically, if we're going to be picky enough about needing the fake-headlamp fixture, then none of the production models are going to look 'right enough'.
The production deltic models would make fine base models for DP2 though, of course (DP2 was of course a production deltic bodyshell with class 50 internals), but in one sense, the builtins would make more sense (DP2 lost the angled twin exhaust vents in favour of the exhaust slot that the inaccurate built-in deltics had.