Trying to make a Boston Cream Pie.... is this going to curdle, or cause the eggs to scramble?

I think because there is cornstarch in the recipe the mix will thicken well without having to overcook the combined mixture, bring back to boiling very gradually though. You can actually boil cream without it splitting but the eggs will "scramble" if you overdo the last bit. I would pour the hort stuff on top of the eggs, whilst stirring vigorously.