This is what a amp repairer in adelaide said!!!

"The Two Rock mods are really easy to do (replace 8 resistors with the values shown on the German schematic).
 
But adding a reverb could be problematic.  I can see where one new valve socket could fit on the chassis layout (between the power valves and the pre-amp valves, there is a space, except the speaker sockets stick into it, so maybe not enoughfor a socket and tag strips.  But we need to find space for another new valve socket as well as a small transformer, and it's not obvious where they could go.  The transformer could  fit on the bare space behind the valves, but that requires moving the pre-amp out of the way to drill mounting holes and holes for the wires - that's do-able but fiddly.    I think there is a hole under the OD Trim control on the rear panel where a Mix control could fit, but I really can't see where the second reverb valve could go.
 
Maybe what I can do is the Two Rock mod, which would take an hour or so and cost $5 in parts, and while the amp is opened up on the bench, see if I can find the real estate for the rerverb hardware and circuitry.  At this point, I need to eyeball the real chassis to see how the internal layout uses the space.  Based on the drawings for your amp, I can't judge exactly what the dimensions are for the possible spaces, so I'd rather not try to quote at this time.
 
The lowest risk solution is to build a stand-alone reverb in a separate enclosure, and feed it into the amp using the FX loop.  That solution would require a separate box for the reverb tank and the reverb circuitry.  The power requirements could be slaved off the main amp, so the main cost would be a separate enclosure to match the main head, plus a small chassis, the reverb tank, and the reverb circuit (which would include a footswitch, enclosure, cosmetics, slave power wiring etc... )"

Be great for some advice guys

Cheers