MSR Whisperlite tinkering

The current Int has a cleaning slug inside it – the 'shaker-jet' part. I don't think you could stick this inside a Whisperlite.
But why bother? The Whisperlite is fine – just a redesign of the Int.

I believe the critical item is the jet. The "hole" is a different diameter for kerosene. Also there is a fiberglass wick for preheating with kerosene. The shaker jet is a nice feature but not necessary. One just has to clean the jet more often, using a cleaning wire.

By "convert", do you mean so that it will burn multifuels?
I have run my Whisperlite off leaded and unleaded auto fuel picked up along the way touring in BC, Yukon and Europe in the 80s. Only problem was fuel tube clogging. I discovered that if I pulled the cable 1" out of fuel tube (can be done with pliars or with MSR tool supplied with stove – insert cable through small hole in tool, rotate tool to lock onto cable) and run cable in and out of tube to ream it after every few uses and then flush witha little fuel,the tube stays clean enough to pass fuel. Not certified by MSR, but it works.

Both the wisperlite and international version got upgraded to a shaker jet about 7-10 years ago. The shaker jet can be retrofitted into the older stoves (it's just a needle in the jet). If you only burn white gas / coleman fuel, it's not a big difference. If you have to burn Kerosene or auto fuel for a few days it's a really big convenience.

The main difference between the regular wisperlite and international is the diameter of the fuel line and pre-heat tube. (The burner tray also has a larger hole drilled in it to accept the larger pre-heat tube on the international, but a little work with a round file will work too.

On the international, the extra large tubing keeps it from getting clogged up as often when you are burning kerosene. The Kerosene requires a different jet, but I believe that jet will screw into the regular wisperlite too. If you are planning to use Kerosene, make sure you practice at home 1st and also in the cold – it's difficult to prime. The easiest way to use alchohol as the primer.

Both stoves will burn unleaded gasoline/petrol – but standard auto fuel will have all sorts of additives that are nasty to breathe, gum up the jet (the shaker jet makes it very easy clean the jet after every use) and make your pots tar covered.

Neither stove burns diesel, jetfuel, or light fuel oil very well, or very long between cleanings. If you need that capability for a trip to Mongolia (etc) get a MSR Dragonfly.

Bottom Line: If you have access to white gas / coleman fuel, then I don't see any advantage to the international over the standard wisperlite. And the international is only an advantage if you plan on burning Kerosene (which is the standard available fuel in many remote international areas).

Personally, I'd get a Windpro for winter use if I had access to canisters during resupply and just needed to cook (and melt snow only occaisionally), and a Simmerlite if I had to melt a lot of snow on a regular basis.