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(this may sound a little convoluted, but it is a retro-fit and not a "direct swap")
The WMC-24 will retrofit to a "rope start" model and a WMC-10 has the linkages for an electric start.
There is one more piece required to convert to the (newer) carb - the carb adapter plate (the Tillotson carbs only had two bolts and the Walbro's have four), but the (Walbro) plate fit's the reed cage (exactly) - this adds about 20 bucks to the refit.
With the plate swap, however, you have to deal with re-jigging the manual choke lever.
(with manual start)
On the Tillotson models, the choke lever installed in a bracket on the carb plate. On the Walbro's the lever is supported by the carb itself and the choke knob on cowl.
If you wan't to keep your original choke lever etc in place (which would save money), you can drill/tap the original carb plate to accept the two extra carb bolts which the Walbro needs - that will not affect it's operation at all - and then fiddle with the alignment of the choke lever to make it work with the new carb.
If it's electric start and you are using a an electric (solenoid) choke activater, then you don't have this issue...