The difference in seat tube angle could mean a 1cm adjustment to your saddle fore/aft to achieve an indentical position.
If you're riding a 73 now, and you choose the 74 bike, you will have to slide the seat backwards, effectively increasing the TT length and extending your position. That might not be ideal in achieving a more upright position. The longer head tube will help though.
The best bet is to plan on using the maximum number of spacers (typically 25MM for a carbon steerer) and a stem with a strong upward angle. A head tube extension would benefit as well. Choosing a fork with a steel or alloy steerer might be a good idea too - they can take far more spacers.