the reason i ask is that i know that buying aftermarket lexus lights dont fit drectly in to the 3.5, so i assume that the gen 3 lights wont fit into the 3.5 *perfectly*?

Is there a gap if gen 3 lights are put on a 3.5?

i will venture no because they are same size only difference is slight

They are exactly the same outer dimensions... the only difference between the 2 are that the Gen3.5 reverse light was moved to the bottom inner edges, on the Gen3 there is no room for this and (from experience as I had a set of Gen3.5 lights fitted to my Gen3).

Therefore one can only assume that a set of Gen3 lights would fit perfectly onto a Gen3.5 with room to spare - but then again - why would you? Lol.

But to answer your question I'd say no, there probably wouldn't be a gap, as the innards will be designed to fit both, but the reason they don't quite fit right is the outer shape isn't perfect... however the Gen3 and Gen3.5 outer shapes are identical