I could be wrong but if you go with a late model 235 with the full pressure oil, it will be a big upgrade from the 34 model, but honestly I'm not that familiar with the 207.

The real question is what do you want to do? If you have a museum piece keep the 207 - if not then changing the engine will not really hurt the value.

So go with your gut -

1958 Chevy Apache 3200
bone stock 235
53k miles
3 on the tree