I didn't see a 260 in the range... perhaps the OP has a 360 which is 30hp rated? in any case a phone call or email to BHG/Rigiflex will probably get the answer...
info@rigiflexboats.co.uk
Ahh the above crossed with the OP's update. In the absence of any folks with Rigiflex experience I'd think it should be fine given folks happily used 25hp motors on the 45kg Aerotec SIB like mine and the Rigiflex weighs 120kg. Also I've used a 3.6m similar flattish hull shape grp Bonwitco and that was fine on a 25hp.