Hi Orange – welcome to the list.
You probable already know - drop bars require a shorter top tube, to allow for the depth of the drops.
If you were to specify a bike with a short top tube and then decide to go with a flat bar you are going to need a very long stem. Not sure of availability, the aesthetics might look strange too.
If you start with the long top tube and then switch to drops, like Fredered, then you will probably find that although you can uses an extra small stem you will NOT be able to mount the shifter on an accessory bar. That would leave mounting the shifter either on the bar end with a hubbub or using the Thorn split h'bar.
SJSC / Thorn really mean what they say with there 100day return policy. Don't be afraid to try out the option YOU want and then change you mind within the 100 days.
Peoples opinion of drop bars on a Raven are very polarised – Most have got a flat bar and wouldn’t even consider a drop, due to the problems with the shifter. Yet those that use a drop bar would claim that in practice there is very little hassle using the shifter with drops and the positives of using drops far outweigh the negatives.
Good luck whatever you decide
Ps for the record I use a drop bar – and I am very happy with it.