Noooo,.... Then you can't pressure test it,.....
You need to isolate the block, from the rest of the coolin' system, 'n pressure test, Just the block,.....
Ayuh,...... Welcome Aboard,..... Change the prop,.... The prop, 'n it's shaft is the only thing that is affected by shiftin' into gear,....
'n you know the 26" pitch is too big,.....
Ayuh,.... Welcome Aboard,...... 'bout the only way to crack cast iron is to freeze it with water in it,.....
I suggest you pressure test the block, before ya spend any money,.....
A cracked manifold will not put water into the oil,.....
Ayuh,..... There's only one length of shaft,....
There was a shorter shaft used back in the '70s for in-line GM motors, 'n the MC-1 drives,....
'n it was 'bout an inch shorter,....
Ayuh,..... Welcome Aboard,..... My guess is, the valves weren't adjusted,....
At All,......
That's what happens, from attempting work, without the required knowledge,....
Ayuh,..... Welcome Aboard,..... Check the starter bolts for tightness,....
The differences 'tween automotive, 'n marine are purely internal in the old style starters, 'n no differences in the PM starters,....
Ayuh,..... When the batteries were installed, were the wirin' ends rubbed with sandpaper,..??
How 'bout at the starter,..?? Ground connections,....
Check the contents of whatever fuel filters ya got,.....
Pull the gas line off the carb, direct it into a catchcan, 'n roll the motor over on...
Ayuh,.... Sounds like weak or dyin' batteries, or extremely corroded connections,.....
Does it start after pumpin' the throttle,..??
If so, it sounds like a fuel delivery issue,.....
What outdrive, or other drive is this,..??
Ayuh,..... Ignition power in, 'n out to the fuel pump,.....
Jumpin' it, by-passes it, Yes,.....
Which carb do you have,..??
As Rick says in post #7, the Weber is known to leak internally, causin' the symptoms yer sayin' yer seein',......
