No, the block is first. GFI is rolled for after the player has moved to the square he wants to GFI to.
LRB6 page 20:
GOING FOR IT!
When a player takes any Action apart from a Block, he may try to
move one or two extra squares over and above the number that
he is normally allowed to move – this is called ‘going for it’ or
GFI. NOTE: if a rule refers to a player’s ‘normal movement’ do
not include the one or two GFI squares.
Roll a D6 for the player after he has moved each extra square.
Note the d6 is rolled after the move.
I think you're thinking of a Blitz Action, in which case you DO roll the GFI before you block because you are paying for the movement square to push back up front. B&C is a Move Action, not a Blitz Action (or even a Block Action) and you therefore move into the square (which may include rolling a block) then roll as per the GFI rules above.
Confirmation from former BBRC member: http://www.talkfantasyfootball.org/viewtopic.php?p=730993#p730993