The 340 will bolt right up to your 904 tranny. It might be prudent to have the transmission rebuilt with high performance stuff so it can handle the torque and power of a 340 engine, a stock 904 with lots of miles will not last long behind a stronmg 340 driven hard!
The 7.25" rear might not last long also. Also check your driveshaft, my 67 cuda came with 273/auto/7.25"rr and it came with driveshaft that was a two piece arrangement. It had a inner and outer tube with rubber sandwiched in between. You should chech to see if yours is like that. I wimpy driveshaft like that won't last long behind even a stock 340!
When I converted my 67 to a 340 in the 80's I used the engine, trans , rear and suspension from a wrecked 340 duster.
Bob
PS: you will need to replace the drivers side engine mount or use a spacer and a longer bolt on one of the three bolts that attahces it to the engine block.
