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The 307 has a small cylinder bore, 3.875" and a stroke of 3.250". The 307 shares the same stroke as the Chevy 327. I'm not 100% positive, but I think starting in 1969 the 307 would have the large journal crankshaft. If your 307 is a 1968 then I'm thinking the crankshaft would be the small journal design. The small journal 1968 Chevy 307 3.250" stroke crankshaft would not fit a 350 block. If your 1968 307 has the large journal crankshaft, then it's worth more than any boat anchor could ever hope to get at a garage sale. The short stroke of 3.250" will allow a SBC to build RPM's fast, and makes for a real good 1/2 mile dirt track engine. The short stroke of 3.250" is not the torque monster stroke of the SBC. The SBC 400 crankshaft has a stroke of 3.750" and is the torque monster crank of the SBC. The SBC 305 is really better for mileage and overall performance than the 307. If your 307 is running good, keep it. When your 307 dies, then replace the 307 with one of the better SBC's made after 1969.

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