I have a top flight SE5a kit I will be building soon (.40 to .60 size) . they dont really say if that is 2 or 4 stroke but I am assuming 2 stroke. I was thinking about using a saito 72. I was looking for recomendations since this has such thin wings and functional rigging wires

Sounds right . Just fly it scale.

The model will fly with that engine as long as you keep the flying weight within the range specified in the instructions. You will also absolutely have to use the flying wires. Make sure you have everything rigged properly, because the flying wires do not only support the wings in flight and on the ground, but they also affect the twist of the wings. You'll need to make sure the wings are absolutely-straight before you try to fly the model.

The model is actually a very nice-flying airplane once everything's properly assembled and aligned.

Sounds like a Saito 62 four stroke would be more appropriate ? I know one person said they were using a 56 four stroke and were fairly happy. Another gent was using a Webber 40 two stroke (nice old engine) and stated it really was under powered. I was using the old take the 2 stroke size and multiply it by 1.5 to come up with a 4 stroke equivalent. a 62 is probably closer to a .35 2 stroke so I went up one size. I will have to check weights now but I was guessing they are lighter than the one days gone past.

(I haven't bought anything yet so I have time to bounce things around. )