I don't think I would put anything on the front oil seal. You don't want that stuff breaking off and getting stuck in an oil passage.
As far as the rear main, it is your choice. I've heard that the rubber rear mains have had issues with tearing apart. Not sure if that has been resolved or not. I used rubber on my rebuild, but that was a number of years ago. Maybe someone who has done a rebuild recently can chime in.
The specific problem with the rear main is the rubber seal has been sold in a form that is undersize for some cranks. What happens is the seal wipes away any lubrication and starts to heat up the crank where it rides. The heat expands it more, and eventually the seal gets wiped out or the crank locks up due to lack of lube and clearance. The seal has been sold in most quality USA made gasket sets for years and the manufacturer has ignored the problems, only saying some military motors are not designed to take the rubber seal. Most of the guys just find a rope seal and install it, properly installed they can be leak free and poorly installed they will drip a little bit. A small drip is preferable to a locked up engine, however.
If you do a Google search on flathead 134 jeep rear seal problems I'm sure you'll find more than enough reading to make you want to build a Chevy instead. Ask your supplier if they know about the seal problem, and if they do not.....don't buy your gasket set from them unless you KNOW it has a good seal.