I have an old Tamiya thundershot that had been modded with a 12 turn modified motor etc, It has all the camber, castor and rolling height adjustments and a shaft drive for the 4wd as it is it can light up all 4 wheels on tar seal with offroad tyres will it be any good as a drift car if I set up the ride height and camber correctly?

It should work fine with some different tires on it, try some abs/pvs piping. Also stock class 27Turn motors have more bottom end torque that a modified, look into getting a stock motor too if you plan on converting it to a drifter. Good luck.

Thats not entirely true, basic electrical theory, the thicker the cable the higher the amps it can carry the higher the amps the stronger the magnetic field enduced in the motor winding, the stronger the magnetic field the more torque you have so a 12 turn motor having thicker cable used on the motor windings has more torque than a stock 27 turn, I have a stock 540 motor also but the 12 turn managed to snap a driveshaft when I used the car on the road with race ofroad tyres on it, the stock motor was unable to get all 4 tyres to light up.

Your amps are then limited by your e.s.c and batterys. Stock motors are proven to have more low-end torque than lower turn modified motors. Perhaps your 27t stocker was worn or low quality, and the modified motor new and top end?

the 27 turn was brand new tamiya gold spec the 12 turn is old the esc is good for up to 30 amps (home made) and the batteries are nimhi 3400mah high output so there is no limitation from these components on the amps getting to the motor.

How many of us run home made e.s.c's and 3400mah 'high output' cells? That's doesn't say much either, you could've been overgeared with the stock motor and harming it's potential performance...

same gearbox setup on both motors

That's a big problem, a 27T stock motor needs to have lower gearing than a 12T mod motor. Running a mod motor with stock class gearing takes away from its top speed, but then again drifting an electric isn't fast or about speed.