My 2001 Nissan Frontier (2.4L 2WD 5-speed manual) has the black plastic EGR-BPT Transducer (part # G28014). I tested it according to service manual procedures and it appears be to shot.

For some reason, these later plastic BPT units are no longer available, but the older (pre-1999?) metal BPT units are still available.

Does anybody know whether the older (metal) BPT units will fit into the same bracket as the later (plastic) BPT units?

I'm really hoping I can get all the parts together so I can do the repairs in one day, because it is my only transportation.

The truck runs fine, but it only gets 20-21 mpg in mixed city/highway driving. I just want to make sure that I'm getting the best possible gas mileage as long as I am still driving it.

If the emissions parts become unavailable or too expensive, I'm thinking I may as well just eliminate (block) the whole EGR system. Does anybody know how blocking the EGR system entirely would affect the mpg?

Dunno about fitting the BPT, but if you're in a non-inspection state, EGR can generally be blocked or deleted with impunity. EGR has only one purpose, to limit NOx formation. It does that by bleeding "dead" exhaust gas containing little oxygen back into the cylinder, which reduces the high temperatures that create NOx. For that reason, you may find you need a colder spark plug range after the delete. Check after 500~1000 miles, a healthy burn is something between burnt orange and cocoa brown. Beige or white means too much heat, so go a step colder.