Cgoligher990

Seems like you need a 16 hp engine

A bigger Kohler engine is certainly the fastest/easiest/cheapest way to go..

Other than changing the bore, there isn't a great deal you can do. Cheaper to put a bigger engine in first

fastest thing you can do to get more power out of that engine is removing it and put a bigger engine in place instead. offcourse you can rule out the governer and risk over revving it till the build in rev limiter kicks a hole in the engine.

just had a look and I think there 1975 models

on early models its usually under the dash panel on the hoodstand, look at the steering column and then follow that line below the dash. Failing that either side of the alloy dash panel

Chris is right, either Commando 7/8 or maybe slightly earlier perhaps an 856 or summat...

Sneaked a few bits out of the van during the day.
found a new starter, fuel pump, carb rebuild kit, brake band and other goodies 

looks like it woundnt pull the skin off a bowl of custard to be honest! suprised it can turn the oversize wheels, it looks like a 2hp honda, plus because he's changed the engine it wont run pto attachments anymore, the bonnets been hacked for the fuel filler, andf the thottle levers been bodged , but these are just points to haggle the price down with, i've bought worse!

that engine looks way underpowered for it! 

Looks like a commando 7 or 8, but has the wrong engine ,no belt guard and the rear fender has been lifted up to clear the oversize tyres. has the bonnet been hacked about where the fuel tank filler is sticking out ?