Farish Brush 4 to pre-TOPS. Backdate or update?

[Colossus]

In N gauge, I want to run a circa 1968-70 class 47/Brush type 4 in green and with full yellow ends.

I'd really like opinions on which model to buy to begin with- the Farish D1572 (green with small yellow end but the incorrect roof louvres) - or a post TOPS blue one with correct roof but plated over headcode?

 

Has anyone experience of 'backdating' a plated over headcode to four digit style? Or conversely, is the later two segment roof louvre available anywhere as a detailing part? I'm certainly not looking for jobs like chopping roof parts out. I'd really like to discover that backdating a plated over headcode to four digit isn't all that tricky allowing me to use the blue Farish one and repaint.

 

Would love to hear of modeller's experiences in this. Thanks.