How low your pump will pump is an open question and I can't say. I have never seen a series belt pump??!!
The gauge you have is worthless for vacuum work. 1 torr is just a few paint flecks wide at the upper end of your gauge. (you can't read it). For fusor work you need 1/1000 of a torr reading. This requires at minimum a thermocouple gauge (~$300.00 new)
As long as the bell jar you have is sealed well and there are no gas leaks it will be sufficient for a demo model fusor, but probably not a neutron producing fusor.
Richard Hull
Created on Thursday, February 22, 2001 4:55 PM EDT by Richard Hull