The coil in the brake line is to absorb movement, hence reducing the risk of fracturing of the line either from movement in the vehicle or when removing and refitting the brake master cylinder. It is good practice.
These are not "factory" parts per se, the brake pipe is bent into that shape by the fitter. All you need is a length of brake pipe, the fittings for the ends, a flaring tool and a round object to carefully bend the brake pipe around. Care is needed to avoid colalpsing the pipe and there are pipe bending tools out there which will do the job properly, though with some care and slow deliberate steps you can do it without. Don't use pliers, they will cause the pipe to bend over.
The "proportioning valve" is the Combination Valve. It has several functions but is a pressure differential and rear brake proportioning valve, and it sounds like you have one intended for front discs which require relatively less fluid than a drum. This MAY fool the valve into thinking you have a leak on the front. To be safe I would replace it with one intended for drum brakes. If you want to keep it there is a button on the right hand side that you need to have held in during bleeding, there is a tool but a helper with a large screwdriver could hold it there. Often during bleeding the flap valve is not activated by the bleeding process so often it does not need to be held, though I am not sure this is good news.
The pulling may be a wheel cylinder issue but more likely is adjustment. I will NEVER have front drum brakes through choice, they are a PITA.
You will have to bench bleed the master cylinder, are you aware of the procedure?
BagusJeep lives in Bali.
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE