I run Clifford street rod headers on the 250. 2 separate 3 tube headers that have the collector flanges ending at about the oil pan flange of the block. There is no way to get direct heat contact to the intake with this set up so generally a water heated plate from Langdon's or someplace is used under the intake. I do not run any kind of heat under my intake, others have had to and others have not.
The adapter you are talking about is an alum body with a non metal insert which is argueably better than an all non metal adapter but I like things simple and inexpensive and would use a basic all alum 4 hole job from where ever you can find one.
You already seem to have the other kind and since you have a stock exhaust that bolts directly under the intake you might be ok as I have found over the years that the Edelbrock carbs when set up correctly are less dependent on the heat than the Holleys for our applications.
