I installed a Passon OD transmission last year in my 70RoadRunner..
Yes there is a gap between 1st and 2nd, think about like having a 3 speed and an OD 4th gear..
Its gears are very close in ratio to that of a Torqueflite. For me the Passon OD transmission is just fine for cruising around.
And yes the gears are noisy for the 1st 500 miles but in my case they did quiet down, but be sure to use standard 90/140 weight gear oil no synthetic...
In my case, I wanted a quality 4 speed transmission strong enough to handle HP but I didn't want to install a rebuilt 4 speed using 50 year old gears.
Jamie Passon was very professional and responsive, it took about 2 1/2 months to get it including shipping to the West coast..

Just my $0.02...