A stock 72 340 was only 245hp net. The stock 3.6l has over 50hp more net hp.
So take a stock 72 340 + Cam and headers to add 50hp and you're at a bone stock 3.6L net Hp
My stock 3.6l Dart ran the 1/4 in ~14.3 @99mph(w/ a terrible 2.2 60ft)
A Good 1/2 second and 5mph faster then a brand new 100% stock 72 340 Duster ran back then(14.9 @94mph)
So again, add Cam and headers to the 340 and the 1/4 time/mph would be similar.