I would not bother with Jenolite. Unless all rust is mechanically removed, it will be back within a year. Been there, all to often.
The reason I would not even attempt to wire brush or use any other form of abrasive on the subframe is that there are so many inaccessible areas, where rust will already be lurking. Chemical processes involving stripping, derusting and E-coating will work, but galvanising is probably not going to be any more expensive and is at least 10 times better. It is good to use a primer for zinc (not a zinc based primer for bare steel), ane a few coats of your favourite epoxy primer, stonechip and top coat over the zinc, for appearance and to preserve it for even longer, but even bare galvanising will last a very long time.
The galvanising process involves an acid dip which will remove all rust, before the zinc dip.
Make sure that you do anything else that may be needed, such as seam welding (highly recommended) first. And, don't forget to have the "camber" brackets galvanised too. They are quite thick and don't usually corrode seriously, but really can look ugly when they acquire a film of rust.