stikpusher
No detail set is available is designed for the kit aside from an old long OOP Lo Model set that is more of a conversion set to make it an A2GA2 or A5. You could probably cobble together some upgrades to the kit using different "accessory" type sets such as jerry cans, pioneer tools, crew gear, etc. Plus you'll have to do some scratch work to correct shortcomings.
The Lo Models set was designed for the older Tamiya M48A3 kit and older Tamiya M60A1 kit. You could turn the M48A3 into an M48A5 or a West German "M48A2GA2" but even the instructions show the A3 side loading air cleaners.
I'm using it with this very Monogram kit I got from the clearance aisle at Hobby Lobby for a whopping $7.50.
The Lo Model set also allowed you to turn the old OD green Tamiya M60A1 into an M60A3 or M60A3TTS, but once Tamiya released an M60A3 and M60A1 RISE/Passive, the conversions were rather useless.
One of the issues with the old Lo set is that you could either use the parts to update a Tamiya M48A3 into an M48A5, or you could use the parts to update the Tamiya M60A1 into an M60A3/A3TTS, but not both since they share some common parts (air cleaners and the gun mount).
But the M48A2GA2 uses completely separate parts and you're right, it is best used on the old Monogram kit rather than the Tamiya kit.
As far as a better M48A2, Revell of Germany released three versions of the M48A2 which are all new and much superior to the old Monogram kit (of 1959) or the Tamiya M48A2 (1981).
They released the M48A2GA2 (03236), M48A2/A2C (03206), and M48A2CG (03287). The A2GA2 and A2CG only include West German markings and the A2/A2C includes W. German, US and IDF markings.
I would suggest building it out of box and enjoying it for what it is. There are too many better M48 series kits to spend additional money to upgrade it. The costs of the upgrades will equal the price of the better Dragon or Revell M48 kits.