Just rebuilt boat motor replaced crank pistons reeds and bored it 30 over decked the heads and after the break in process It will only run 55 at 5000rpm and before it ran 72 at 5800rpm whats wrong.

Assuming you could get the motor to unlock, it would require a complete overhaul in order to run properly again because either the crankshaft bearings or the camshaft bearings (or both) and possible the pistons themselves have welded themselves to the engine internals. Most likely a new crank, cam, pistons as well as having the block bored and resurfaced.....get the drift?

when setting up the valve timing it is always done on the exhaust stoke.. Place the piston on TDC and set the valve timing so that the exhaust valve is just closing and the inlet is just opening. Rocking the crank a bit before tdc to a bit after tdc will produce a movement where the exhaust starts to close as the inlet starts to open. This is known as valve rock or valve overlap. The cam modification is of no consequence as the as all that is modified is the valve duration , not when they open or close. With the cam now timed to the crank turn the crank 180 degrees and set the ignition timing to the degrees advanced recommended ( 10-12 degrees bftdc is recommended for starting). Place the HT leads in the correct firing order and when running use a timing light to adjust ignition timing. If you are fitting a new cam then you must bedding in grease and when the motor starts it has to be run at around 2.000rpms for around 10 minutes to set (harden) the cam lobes or else they will wear off very quickly.

If you have excessive blow by and the oil is coming out then I would consider it time to replace the motor or have it professionally rebuilt as you have piston /ring bore wear problems.

It is possible the valves could hit the pistons and were bent. Another part that may have been damaged is the crank angle sensor located off the lower belt gear on the crank shaft. A dealer can tell you if your valves get damaged when the belt breaks on your model (on some engines the valves do not contact the pistons when the belt breaks).You can line up the timing marks and replace the belt yourself. Before reassembling the motor, run a compression test to see if the the head needs to be repaired. If your compression is still 110 or above on all cylinders (and with in ten pound pressure of each other) your engine should run when you put it back together. When you are replacing the belt you can inspect the crank angle sensor for possible damage.

replace trottle poss.sensor

yes new heads are in order sorry

Running on a stand is not the same as running under power...In the water, you are essentially running on a dynomometer (dyno is a big water brake) If you can prove that the module isn't putting in enough advance, it would be doing the same thing that I mentioned with the damper, only for a different reason. So...you're likely on the right track. (rather have a points setup out on the water...anything goes wrong, you fix it without a tow!!!!)
Good luck

Lost of compression is due to either leaking head gasket, valves not closing and seal properly or piston rings are worn and need replacing. One can tell if you have bad head gasket, oils contaminated by water when looking at dip stick, bad valves cause some smoke and run rough, worn piston rings will cause lots of blow-by and will cause white smoke heavily and also runs rough. Being 1968 original motor and never have been rebuilt will probably have over 100k mile will be needing tear down and rebuilt. Rebuilt it correctly will get another 100k plus. being 1968, doing your head and valves job or replacing head gasket if that is the problems and you can get by it. worn rings, I would rebuilt it completely instead repairing one or two cylinder unless you plan to get rid of it.

check your timing. might be to far retarded

pull the valve cover off and look for your self, is it running?you prob need too get a second oppinion
it could be as little as just replacing the valve or a whole head too an engine or maby thats not even the problem what did the car do?