Hiwatt Bridging Modification for 4 holers....

Gassage

I was looking at @meltedbuzzbox 's amp pics. I noted the bright/normal bridging he'd done.

To do this well, there's a little mod inside needed. here's the diagram. @ICBM may have a view too.

ICBM

I'm not sure why you need to. Just linking them via the inputs as normal does the same job.

You don't want to do away with the grid stopper resistors either, assuming you haven't just left them out of the drawing for convenience.