yes they have diffrent parts inside, but it's not to the point that a 160 pump is going to limit you very much. Most any of the mods you'll be doing to your 160 pump you would have had to do with a 215 pump. I've seen guys cranking out well over 500 hp who started with a 160 pump.
The 215 pump does have a slight amount of timing advance to them from what I've heard (4 degrees was the numer told to me) but for 95% of the folks out there building a hotrod, the 160 pump is every bit as good a starting point as the 215.
George
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1997 2500 ext cab long bed 4x4 Boost control elbow, KDP tabbed, silncer ring MIA, Z-series gauges, 47RE built w/valve body & converter, #100 plate.