Assemble the circuit on a good quality PCB.
T1 can be a 230V primary, 35V/3A secondary step down transformer.
If 3A Bridge is not available, make one using four 1N5003 diodes.
LM317 must be fitted with a heat sink.
R2 = 0.85 ohm is not a standard value. You can obtain it by combining a 6.2 ohm and 1 ohm resistors in parallel.
F1 can be a 2A fuse.
To setup the charging voltage, power ON the charger and hook up a voltmeter across the output terminals and adjust R4 to make the voltmeter read 28V. Now the charger is ready and you can connect the batteries.
This charger is specifically designed for two 12V/7AH/6 cell lead acid batteries in series OR a 24V/7AH/12 cell lead acid battery.