Has anyone tried using the MSD timing retarder that has boost reference to pull more timg out at higher boost levels ? Or would I just be wasting my time any money and hold out and save up for a stand alone ?

 

Well, you'd need 3 of them, one for the leading, and one each for each trailing, otherwise you would retard just the leading and send the car into negative split under boost. Then you'll be walking home.
As well, you need to connect to an ignition box, so you;d need 3 of them, too.
At that price (3 x 228 for the BTM's, and 3 x 184 for the 6a's, for $1236 total), you could easily afford a stand alone.
As well, these cars are pretty boost limited on their fuel map just as much as they are by their timing map. The timing map will retard fine for as much boost as the stock ECU can provide fuel for.

The boost timing retard units were desgned for cars with a distributor.