I have a friend locally who carried a Garand through the Korean War. He's in his 70's now, and still loves the Garand. Anyway, to cut to the chase, he decided that he wanted a Garand in .35 Whelen. He was able to get a local gunsmith to do the conversion, and it's a good one, but he's never been able to get the rifle to be 100% reliable. The gunsmith thinks it's something to do with the op-rod: just as if you shorten a Garand to Tanker configuration, this messes up the action, the same seems to happen when you go "overbore" with a bigger round. He says he can usually count on at least one malfunction per clip, sometimes two.
His conclusion, and that of his gunsmith, is that the Garand is best left in .30 caliber (either the original .30-'06 or .308), as that's what the action was designed for - and even in .30 caliber, concentrate on bullet weights in the 150gr. range. I would agree.