340ci vs 360ci engine

The 360 has a little longer stroke which helps with low-mid RPM torque. If you're gonna drive the car often and in traffic you'll like the 360 better. Figure you'll get about the same power out of each with the same parts, but the 360 will do it 500 RPM lower.

Actual build-up costs will be similar between the two, but 340's are getting harder to find. If both are available for the same money, the 360 is probably overpriced. I'd do like Joe said, sell the 340, build a 360 and put the extra into a nice converter or something. You'll have a better car in the end.