Aled Owen wrote:
I have a lawn which is simply too big for an electric mower to cope
with, also I hate having to mess around with the cable all the time.
Rather than buying a new mower I've looked at Briggs and Stratton
engines as well as Honda engines and it seems it would be cheaper to
buy an engine and adapt it to fit the mower.

Has anybody done this before, is it actually possible? It's got a
steel chassis not some cheap plastic rubbish (ironic considering it
was pretty cheap mower).

The only problem I can see so far is having to replace the sproket
(and perhaps blade) because the Honda engines seem to have a bigger
output shaft diameter than on the current electric engine (I've not
measured it yet I can't find my depth gauge D:, all in good time
though)

Any help would be appreciated

Go search freecycle or craigslist for a free/cheap gas mower.

I've never seen an electric built heavy enough to handle a gas engine. Chassis,
wheels,.....

Re-furbing an old gas mower would be a way easier job.