I would start out with my 7" grinder and get what I could with that, then down to the 4" for a little more access, then probably have to finish with the pneumatic die grinder with a thin cut-off wheel.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy