@clothmama can you access the 120cm bed from both sides? If so I would continue with the 2 rows. I wouldn't worry too much about getting the 35cm exactly correct at the base between the two rows in the middle as remember when they start climbing they ll grow away from each other.
If you can access either side of the bed you will be able to reach your arm through from one side to the middle bit, maybe leave a small gap to send a small Remy sized child in
Again remember they will be growing in a triangle and growing towards your arm as they grow up iykwim. Seriously the beans will hide whatever anyway
It might be that the ones in the centre rows will get less light and not produce as much but I d just give it a go and see. Maybe plant in succession with the middle two rows first and give them a head start so that they get the light? Then plant the outer rows 1-2 weeks later? Could give you a longer, staggered run of beans too.
I m kind of trying to do that on my little bit.