Manual valve body W/O engine braking?

The difference you're referring is the "low band apply" feature, on a full manual valve body.
A low band apply body WILL have engine braking in all three gears. A non low band apply, will freewheel in low gear only, if power is removed (you take your foot off the gas. )
Low band apply is much safer for the trans, and your feet, non-LBA is supposed to be (microscopically) faster/quicker.
Any full manual body, either reverse or forward will simulate a stick shift somewhat, cause you will have to make EVERY shift, up and down yourself.
A custom shifter is not necessary. I daily drove a 440 rr with a reverse full manual body, non-LBA, with the column shift for years . (I have three cars with full manual valve bodies, and another car gonna get one, with a transbrake).
Edit: shifter. As above, my rr uses stock column shifter, 62 uses a B&M pro ratchet, Cortina uses a modified Cheetah for the glide with a transbrake,(was used in the 62 with a 727), and the opel also uses a pro ratchet for the Turbo 400 transbrake.