Hello, first thank for your interest and welcome
# syslinux-install_update -iam [3]. (does obarun provide it too??)
this is the exact command line used by obarun-intall script to install syslinux :), but if you usualy use grub, you can use it with obarun too (grub is available on the iso :)). i will explain you how to make it.
i assume that you will use obarun-install to make the installation and you are under the iso
Well you need to edit the file /opt/obarun-install/config/obarun/customizeChroot, for this open a terminal a tape this :
$ sudo nano /opt/obarun-install/config/obarun/customizeChroot
and comment those lines at the end of the file :
# echo_info " Installing bootloader: syslinux"
# syslinux-install_update -iam
# echo_info " Maybe the partition name in the root parameter needs to be replaced."
# echo_info " Be sure to point the root partition in the line APPEND."
# echo_info " The editor will be launch in 10 sec for editing file syslinux.cfg"
# sleep 10
# "$editor" /boot/syslinux/syslinux.cfg
# echo_info " Customization terminate"
save it and exit
prepare your partition as usual and make the installation like describe in the obarun wiki
after this you have a complete intallation on the device without any bootloader (edit : i mean syslinux AND grub is intalled)
So now you need to chroot the new installation to install and make your desire changement for install grub (i assume that you have mounted your device in /mnt)
$ sudo arch-chroot /mnt
now you can install grub as you make it as usual :). When finished exit of the chroot
$ exit
finally reboot
Syslinux can make the same thing but i'm not an expert about dual booting with windows, so i cannot provide you a good advice about it, however obarun or archlinux about bootloader apply exactly the same thing, so you can follow the arch wiki if you want without any special changement for obarun :).
i hope this explanation help you