$6,000 - WHEW!
Six grand to rebuilt an A-4 sounds pretty high. I friend of mine just replaced the anemic 11-HP Universal diesel in his C30 with a brand new 25HP Universal, at a cost of about $5,500 for the motor, plus installation of about $1,000. If you want to replace with an OB, you'll need a pretty big one to push the 10,000 pound C-30 at any speed with a reserve. I've got a C-27 with a 2000 15HP Johnson 2-stroke in the well, which replaced a similar 9.9. Both motors are fine in my boat, which is about 6,000 lb. The 15 has more reserve horsepower when punching into seas or headwind, or pulling the dink. It comes at higher fuel usage, about 1.25GPH at 2/3 throttle, which is about 5.2 knots on my 27. I would think you'd want at least 15HP, maybe 20. As I recall the A-4 has about 30, which is about right for the C-30. You'd also have the hassle of a transom bracket, and the resale value of a C-30 with an OB would be quite low, I would think. If it were me, I'd look for a lower cost rebuild, or consider a new diesel. Try Moyer Marine (they're somewhere in Pennsylvania-check the web for them, or Good Old Boat Magazine.). A-4s are all they do. Parts, advice, and rebuilts. Good luck
