F1 v F2?
MTOW is increased on the F2 by letting you have a little more power below about 40 knots. The increase from memory is about 120 kg. The F2 also has the hydraulic over centre accumulator in the yaw channel so you can maintain control if you lose that hydraulic circuit.
OEI it won't matter much as the engines are the same and the F2 can be heavier.
C20F's are the same as a C20 B. Difference is only the gearbox which is very similar if not the same as the B17 turbo prop engine. In fact without a lot of difficulty you can probably mod a B17 to C20F.
If you already have Short Rangers then your maintenance guys will be familiar with the engines. There is a large amount of commonality except for the PTG's.
Depending on the climate the Allisons are prone to oil leaks due to the close cowling of the two engines. Get geared up to change gearbox lip seals regurlarly.
Another unfortunate is the Allisons tendency to have the N2 speed wander around with the met conditions. This doesn't help with keeping the rotor "on speed" where it is smooth. It is also imprtant to try and keep the droop compensation of the two engines similar. Also be sure the engines "top" as they should.
It is possible to fit C20R's but you would have to be brave.
Ice and 355's do not mix. Ask the Brits.
Electrical systems tend to be neglected and are obviously nearly doubled over a single engine Ecureuil.
Your tag indicates Iceland so the OEI performance should be reasonable.