Good morning Odysseus,
The boom on my Bav 38 2003 is total from cold to the mast groove till end of boom 497,5 cm.
The turning axis near the mast is at approx 4 cm from the mast. For the main sail dimensions, the measurements are from mast groove till start of tensioning indication 450 cm and till end of tensioning indication 474 cm. (my mainsail bottom luv? is 465 cm). From end of tensioning indication till end of aluminium of the boom is 14 cm. The last section where the reef rollers are in is 9,5 cm. All this adds till the total of 497,5 cm mentioned above.
Hope this helps.
Ger