You can't get that BMW look, that is you can't get it easily, bonnet would need to come further ahead and have more V-shape when looked from above.
Manta 400 had round double lights while having similar angle (well in one direction) of front as 300, but still there shape continues at bonnet/fenders, having such straight front as 300 has with bumper coming forwards and bumper's close to lights edge rising upwards is making thing look wrong, so it would require whole new design of front to look good, imo.
Bumper, bonnet at least need to be shaped again, of course light shrouds are needed to be made as well has front grill.
GT/E
400
Making front cone, modifying bonnet, making new fenders that are more puffed out to fit wider rubber, then I would not see problem there, it can be made to look good, but is it what you want? That way you could of course find bit additional space for coolers/fans, but it is not very wide car and making longer front end can make it look stupid, so, imo, it needs then those puffed out fenders to make it look right and not narrow + long.
Volvo 360GL -88 -under restoration-
Volvo 343DL vario -81 -running-

Volvo 240 Diesel -83 -undecided-
Citroen ZX Dturbo -97 -daily-

