If you have the 400 crank use it and put it back together as a 400. You'll be glad you did later especially after you drive a well tuned 377 and a 400 back to back on the street. I prefer using 5.7 rods too. Stock chevy 5.7 rods almost always hit the cam on 3.75 stroke applications. If you can afford it buy good rods. If not grind yours to clear your cam and have the assy balanced after you finish grinding. 377 are great Modified dirt track engines where the engine lives between 5500 and 8000 RPM's. For the street I'll take the 400 anyday, more torque and HP between 2500-5500 will equal a bigger smile on the street.