well a 273 vs 340 is maybe 10 lbs difference, I would guess.
As for the transmission, the car when built came with one. ;)
OK, here is NHRA weights.
http://www.nhra.net/tech_specs/classification/index.html#ply
VALIANT 1965
170 225 225 273 273 273 273 273
* ** * * ** * **
Std Auto
101hp 145hp 145hp 180hp 180hp 180hp 235hp 235hp
100 106
Sedan 2 Dr 2527 2527 2527 2707 2707 2707 2707 2707
Sedan 4 Dr 2581 2581 2581 2761 2761 2761 2761 2761
Sta Wag 4 Dr 2756 2756 2756 2935 2935 2935 2935 2935
200 106 0 0 0 0 0 0 0 0
Sedan 2 Dr 2535 2535 2535 2714 2714 2714 2714 2714
Convertible 2 Dr 2646 2646 2646 2825 2825 2825 2825 2825
Sedan 4 Dr 2601 2601 2601 2780 2780 2780 2780 2780
Sta Wag 4 Dr 2756 2756 2756 2935 2935 2935 2935 2935
SIGNET 106 0 0 0 0 0 0 0 0
Sedan 2 Dr Hdtp 2632 2632 2632 2811 2811 2811 2811 2811
Convertible 2 Dr 2716 2716 2716 2895 2895 2895 2895 2895
BARRACUDA 106 0 0 0 0 0 0 0 0
Sedan 2 Dr Spt Hdtp 2761 2761 2761 2940 2940 2940 2940 2940
S/SS Factor 101 135 145 165 165 180 210 230
6.28.05 4.28.05 7.13.06 6.30.08
I don't know, I don't own one, I was just asking a Hypothetical question, if I did own one what it would weigh if I dropped my 340 in it with an auto.