Converting Hartke HA3500 to Ha5500?

[ribafish]

So...the tube in preamp died a few days ago, so I opened the thing up to change it...and I saw that the PCB should be the same as in its strogner brother, the HA5500. The board revision is v1.5_051216. The main board clearly has two 'sides', marked HA3500 main and HA5500 main. Near the front is also written (on PCB) model 3500b 5000 7000b.....but i would be perfectly happy with 5500. To me the conversion from 3500 to 5500 looks doable, so my question is did anyone do anything like it successfully and/or could you share some schematics(I found some but the newest is from 2003) both from 3500 and 5500(some pics of guts of 5500 would also be welcome).
If you think this is not possible/is too expensive(meaning it would be cheaper to buy another amp) please put me off this obviously mad idea.

PS: I'm running a great 410 box rated at 800w rms at 8 ohms and I'm not planning to add another one as this one sounds really great for what I want from it. In this setup it gets only 240w and I think it would benefit from another 100watts.....if nothing else I would have a bit more headroom, so the head would have a cleaner signal.

PS2: I'm planning on installing a passive HPF...where do you think it would be best to put it....I'm kind of leaning towards putting it after the DI(just before the master section), so the power amp gets filtered signal, but the DI is unaffected. Any toughts?

[Jazz P Bass]

The Hartke HA3500 is rated at 350 watts into a 4 ohm load.
The HA 5500 is rated at 550 watts into the same load.
I would think it obvious that a larger transformer will be required for the conversion.
At the least.