Which blower is this and...
 

..can it be bolted on top of a Merc Bulldog?

I DO see that it is a Weiand, but I have no idea which model/size/etc.

The current engine is a 502 -96.

Here's another pic
 

_

It's a 250 (as in cubic inches). It would be alright on a 454, but is really undersized for a 540. For max power, you'd be better off with a 8:71.

The Bulldog is also a tall block so would require spacers for the intake manifold to fit

For a 540 bull dog I agree with the use of the 871 blower. you can use smaller blowers but you have to turm them at high rpm which causes more heat to be generation and a shorter blower life. If you put a blower on a 540 bulldog you want to run about 6psi of boost . If you want to gain more power add an intercooler and increase you boost to about 9psi going into the cooler. The intercoler will add about 50+ hp. Also add a large external oil cooler.