Looking for input from those more knowledgeable than myself. My Dad wants to build a Remington 760 in .358. Am I better off to get a .35 Remington 760 and rechamber or get a .308 and send it off for a rebore?

I think the .35 Rem has an odd head size. If you want a .358 on that platform, get a 760 in .308 and rebore or else rebarrel any of the standard .473 head sized actions. A .270 or 30-06 to .35 Whelen is also possible.

I would have JES rebore/rechamber a M/760 .308. They do good work, fair price and reasonable turnaround time.

I think that a JES rebore of a 308 would be both cheaper and better. Cheaper 'cause 760s in 35 Rem are significantly less common and more expensive than 308s. Better 'cause (I think) you can order a quicker ROT that will allow you to shoot longer/heavier bullets. IIRC, 760s in 35 Rem camwe with a 1-16" ROT and I have been told that they don't work well with bullets heavier/longer than the 200 grain RNs. However, Marlin 336s in 35 Rem are cut 1-16" and my 336SD was successfully rechambered from 35 Rem to 356 Win. It shoots my 2 favorite .358" bullets, the 180 and 220 grain Speer FPs, quite well.

This is often repeated, but insignificant. Remington used the same bolt for 308/30-06 and 35 Remington. The minor difference in head size just doesn't matter.

The twist rate in the 35 Rem barrels is fine. Mine shoots great with 250gr jacketed bullets, and have tried 270gr cast with good results as well.

With that said, a Remington 760 in 35 Rem usually commands a premium price, so if you don't already have one, it might be cheaper to rebore & rechamber a 308 or 300 Savage barrel.