Engine, rear gear, Tourque Converter, Tire size info/question for the experts

on the back;
About the smallest tire somebody might run is a 24 inch, and about the tallest that fits is a 28.
From small to big, that's a difference of 28/24= plus 16.7%
This is thus the maximum difference in your hiwayspeed, both at same slip.
A rear gear swap is a lil under 10%, ie
2.94 to 3.23 is plus 9.8%
3.23 to 3.55 is plus 9.9%
3.55 to 3.91 is plus 10%
3.91 to 4.30, is plus 10%
3.73s and 4.10s are half-gears at about 5%.

As for overdrives;
You got about the right gear for use with the Mopar .69 overdrive.
3.73 x .69= a final-drive ratio of 2.57, and 65= 2100, in lock-up.
But, if yur running headers, that cam will likely suck gas big-time at 2100 in steadystate. Yur a good two cam-sizes too big for 2.57,
OR
a good two rear gear sizes too small for that cam.