Hi Al,
The 15 cwt 41-42 Chevy was adapted from the civilian Chevy AK model, available in 1/2 ton and 3/4 ton versions and several different wheelbases. The LRDG 15 cwt was the 125 1/4 inch wheelbase model The truck sits considerably lower than its larger cousin and the wheels are smaller, with 7.5 x 17 tires. The 15 cwt used a 216 cubic inch displacement engine which is outwardly identical to the slightly larger displacement engine of the larger truck, and the two are interchangeable. I have a photo showing a 15 cwt Medical Officer's truck parked beside two LRDG 30 cwt trucks, and the difference in size is quite evident. I tried to upload it to post it here, but it didn't work. Sorry.
If you can find a suitable set of wheels you may be able to modify the front end of the larger truck to make it look right. The photo Steph posted is of Bill Kennedy Shaw's truck, and you can see that it is quite low to the ground compared to the men standing around it.
I don't think any of the 15 cwt trucks took part in the Barce raid. By then, jeeps had replaced them as pilot cars.
A friend of mine has a 42 Chevy pickup which has military OD paint beneath the present finish. I've tried to convince him to cut the top off, get rid of the doors and convert it to LRDG configuration with no success. Maybe some day. . .
Good luck with your project.
Cheers
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Dick