Hello and welcome to the site.
The Spitfire parts start with the 3** prefix for them. Your part number starts with the 285 what indicates the Wellington Mk.I. The number 57 after the prefix indicates the bomb gear part. The 307 is the part number. Other parts may start with the 290 for the variant. Below there is the list of the part prefix for Wellington variants ...
285 & 290 = Wellington I
408 & 409 = Wellington Ia
415 & 450 = Wellington Ic
298 & 406 = Wellington II
417 & 440 = Wellington III
410 & 424 = Wellington IV
407 & 421 = Wellington V
442 & 449 = Wellington VI
429 = Wellington VIII
440 = Wellington X
454 & 458 = Wellington XI
455 = Wellington XII
466 = Wellington XIII
467 = Wellington XIV
Also the manufacturer code of the inspector stamp starts with the "V" letter what indicates the Vickers factory one.
To sum up .. the Wellington part.