I did my top about 10 years ago , So memory might be a little off ;
The top piece of wood slots under those little ears on the back panel ,
The holes on the little ears are for the nails to attach the panel to the wood,
The spaces between the ears are where you nail chicken wire ,vinyl top material, &
finally the metal trim piece, not forgeting to put some sealant in there to help stop leaks !!
You have to space all the little nails carefully to allow space for each layer
I think mine was just like yours you don't get a lot of room .
Slide your piece of wood in there and you should see what I mean !!
Good Luck with it, Mine does't leak ,
Though I do get some water in from around the firewall in a heavy rain but can't blame that on the roof job!!!
John Cochran