According to the datasheet, the FPU in 68-pin PLCC has not one, but eight VCC leads :'( And twelve Ground leads.
However, I think a less intrusive way to disable the FPU would be applying VCC to the /CS input (Chip Select, pin 29 -- third from the right of the top row if the index dot is at the bottom). Doing that thru a low value (say, 330* ohm?) resistor probably won't harm much the associated logic, at least for a brief testing. Desoldering a single J-shaped lead of a PLCC chip doesn't seem a trivial task to me...
*) I'd put first a reasonably high value (≈ 1 Kohm) and then go down gradually until the FPU stays safely disabled. Haven't actually tried this, though.
However, I think a less intrusive way to disable the FPU would be applying VCC to the /CS input (Chip Select, pin 29 -- third from the right of the top row if the index dot is at the bottom). Doing that thru a low value (say, 330* ohm?) resistor probably won't harm much the associated logic, at least for a brief testing. Desoldering a single J-shaped lead of a PLCC chip doesn't seem a trivial task to me...
*) I'd put first a reasonably high value (≈ 1 Kohm) and then go down gradually until the FPU stays safely disabled. Haven't actually tried this, though.