IAWMP and austin. A plan can satisfy a safe harbor that would not actually pass the general test, but these SH allocations (or DB benefit formulas) need to be stated in the plan to use the design-based SH. If you don't have a design-based SH allocation in the plan, you have to pass the general test. Duplicating the results of a designed-based SH is not equivalent to passing the general test.
One thing to keep in mind is that the applicable maximum lump sum may increase as time passes, depending on the details of the situation. I agree though, if you have an actuary look at the specifics of the plan, they should be able to tell you if this is likely to be the case for you client and give you a better idea of the available options.