Micro CoGen.

That was the initial thought.  That's why I made the fancy pictures of it.  I actually sold a few locally but I wound up with more cnc work than I could do so I never put much effort into selling them.

@ Henry
Construction is simple.  It is made of two flat cnc cut plates spaced apart with two rectangular plates.  The two rectangular plates have about 2" of the end bent at 45°.  Stack it up and weld it all together.  See the picture of it not mounted.  The one in the picture only has 4 mounting hole but I made some with 8 holes so you could rotate the mount in 45° increments.  The bolt pattern is one that is on most 3 to 8HP engines.

@ Lloyd
I don't use the Zena a great deal since most of the welding I do is in my shop and I have other welders to perform that task.  But I have used it enough have some opinions. Welding performance is surprisingly good.  Most people have to try it to believe it because it doesn't seem like there is enough to it to actually work.  It's performance is as good or better than any big name air cooled gas powered welder I've used.  One weird thing about it is the weld puddle seems to whistle.  Probably due to the 18kHz pwm power control.  The welding power generator is nicely made inside of a delco 12si alternator case.  The obvious modifications are isolated ground, large power lugs and instead of a regulator, the wires to the brushes come to where the plug normally goes.  12 volts across the two blade connectors = full power output.  The amperage control is in your hand.  While it is handy it is also subject to all the beating and abuse the welding electrode holder takes.  I've managed to break the knob off of mine.  It's not happened yet but I wonder what will happen when the control wires get shorted.  You only work around metal for so long be fore something falls on the lead or it gets melted.  I wonder what will happen to the control box when that happens.  If the control box ever breaks I'll probably just replace it with a 12v PWM dc motor controller.

@ Cornelius
This mount design won't work with the alternator you have.  The mounting holes have to be a 180° apart.

I built it.  About 6 years ago I built a CNC plasma table.  This was one of the "gee I wonder what all I can do with this thing" projects.  Initially I started out making a mount for a Zena welder that I had picked up reasonably cheap.  I built mount for a horizontal shaft engine  that held a zena welder and delco 10si alternator.  The old 8hp engine I put the setup on wasn't quite up to the task so then I made a mount for a vertical shaft 15hp riding lawnmower engine.  The vertical shaft mount was kind of neat.  It was made with interlocking slots and tabs.  I dug up some of the old pictures in case some of you guys were interested.  I don't have any pictures of the vertical shaft mount with the engine in place but maybe you can see how it worked.  Any way, the simple battery charger was the last of my different ways to connect an alternator to a small engine.

How's this for compact?

Here is the start controller I plan to use on my Perkins 402 project.  I haven't bought it yet because I'm not that far along. 
http://gencontrol.co.uk/index.html

You can order it with custom parameters.
http://gencontrol.co.uk/Generator%20Control%20Module%20Creator%20for%20advanced%20engineers.html

The the price is right too at £60-£70 depending on the model (about $98-$114 currently).  Some options like the battery voltage monitor drive the cost up a bit.

If anyone here has used one of these I'd be interested in their opinion of it.