Yes, a Mazda B2000 is most definitely a 4-cylinder with a 2.0L engine. However, technically Mazda didn't produce the B2000 as a 1988 model. It was made in 1986-1987. Then in 1989 Mazda made the B2200 Pickup, which is a 2.2L 4 cylinder.
Attached is a link with instructions to install a weber on a Mazda B2200 or B2000. These instructions have been modified from the original to be more specific to you're application. Kyrasis6 Owner of Mazdatruckin.com
Yes, this is as easy a swap as you'll ever do. It's the same engine almost; same cylinder head, same carburetor, same starter, the B2200 uses an F2 which is a slightly modified FE which is what you will find in the last few years B2000, I think 84-87.
One could purchase auto parts to repair a Mazda B2000 from the Mazda B2000 Auto Parts online catalog. Other places to purchase auto parts to repair a B2000 would include O'Reilly Auto, Advance Auto Parts and also Auto Parts Wearhouse.