I have a 1970 914 that has everything else from a 1976. I am trying to figure out what size wheel and tires I need to use to not throw off the speedo and gearing. Also, if I wanted to use wider and lower profile, what would be the best to use without converting to 5-lug or flares, and is there a good way to change the speedo gearing if tire size is different?

Probably the most discussed topic on this board. Try a search, you'll find plenty of info.

Short answer: 165x15 on 5.5" (4.5" on a '70) wheel is stock. Using 5.5 wheel width you should use 195/65x15 to maintain stock diameter and therefore maintain gear ratios and speedometer reading. Nothing wider than 165 should be used with 4.5" wheels. 195's are readily available and will not require any fender adjustments. If you still have the '70 speedo calibrated for 155x15 tires on 4.5" wheels (standard in '70) your speedo will be off slightly with 165's or 195's but not enough to matter.