Speedo Gear Questions

My car hasn't had the speedo connected since it was a 198 slant. I now have 4.33 gears in a 9" Ford rear, in my 360/727 74 Dart Sport. I'd like to get the speedo correct.

M/T ET Street 275/60R15's will be ordered before my Summit 10% discount code expires 12-31. (Thanks again, GTXJohn!) The M/T website shows the tires as 28.3" tall. ET Street® S/S

Looking at speedo gear charts, for a 28" tall tire, most seem to indicate a 40 tooth gear, at least one says 41. (For a 4.30) I'd like to get whichever would be closer, but I don't know how to choose.

Also, is there a preferred manufacturer? Summit has Advance Adapters and Rugged Ridge, for two. Amazon shows someone named "La". Then there's Brewers, Classic Industries, Mancini, and who knows else?

Bottom line: I'm trying to get the correct gear from a good manufacturer. I imagine some are just re-branded. I would like to get it from Summit, to include it with my tire's free shipping, and the discount code.

EDIT: It's a 66-up trans.