Sort of - your existing Jabsco toilet bowl and seat will fit right on the SeaEra conversion kit's base. By re-using your bowl and seat, you can usually save between $80 and $100 off the cost of buying a complete new toilet.
That being said, the bolt mounting pattern is not the same from what you now have, hose routing will be different, and it may be necessary to mount the base sideways if there isn't enough depth to install it in the standard configuration (this is very commonly done, see smaller picture:
http://www.raritaneng.com/products/toilets/electric/sea_era.html
In addition, you'll have to run the DC wiring to it. A bowl mounting kit, an inline seawater strainer and a heavy-duty pushbutton switch are all included with the SeaEra conversion kit.
But those issues will all have to be dealt with anyway, if you go any way
other than with Jabsco's add-on electric pump kit, which is noisy enough to wake the dead - plus it isn't exactly cheap, either! This kit bolts right onto the existing toilet base and all you need to do is connect the hoses and run the wiring to it (see electric flush toilet pump, at the bottom right
http://www.boatfix.com/catalog/579.pdf
The SeaEra conversion kit isn't silent either, but it's not nearly as noisy as the Jabsco unit. Jabsco's electric pump kit
is an easier and less-complicated installation however. But I have some doubt as to whether you'd be completely happy with it after installing it. You have to bend down to twist the knob to flush it - your nose is practically in the bowl when you do it - plus there's the noise issue... The SeaEra's pushbutton switch can be mounted anywhere that's convenient - the Jabsco unit has the knob right on top of the motor, there's no option with it.
Jabsco also has another conversion kit, very similar to the SeaEra conversion kit; you'll see it higher up on the Jabsco catalog page linked above. But of the two, I feel that the SeaEra is the superior product (Just my $.02). I'm not trying to snowball you with Raritan stuff, just making a comparison - I don't
always feel that the particular Raritan product is the best - but it often is.
