Brian check your pm's.
Short of it is, if your heads are stock and no porting / flow work done to them even though they are SE aftermarket heads I doubt you would see an improvement with the larger throttlebody. My opinion is that you would burn more gas and see a deficit in HP /TQ. If you had some port and polish work done the flow and velocity of the air would be better and the engine would then be able to take advantage of the additional air mass. The 400 dollars would probably be better spent on 24/37 gearing over 25/36.
Unfortunately though without flow numbers on your heads it is just a guess. I would expect you to see mid 130's to low 140's in flow numbers on your heads. Two sets I saw today were just flowed they were SE HTCC heads and 103+ heads, the HTCC were in the mid 140's and the 103+ were 145 and 148 before port and polish.
If a third dyno tune isn't out of your budget then I would say keep your map from your upcoming second tune. Then go ahead and you and beags install the larger throttlebody take it down for a 3rd tune and if it does fall on its face sell the throttle body with minimal loss and put back on the stock throttlebody with your 2nd tune map. Personally I wouldn't do this in this case, but some of combination making is trial and error and some added expense to know.
You will have your hands full if Mackey sets up Beags with his 630 cam / headwork and his 20 degree pistons. If this happens we will have to rename LD to TV tailight viewer
