rattling noise

[78chevy]

i own a 78' chevy stepside with a 350/350. I obviosly don't know everything about engines, otherwise i wouldn't need your help. When i am in neutral or in park and accelorate there is a rattle that seems to be coming from my transmission? I recently put on a new air gap intake and had a minor internal antifreeze leak. well i fixed the leak and changed my oil many times to drain all the antifreeze but there seems to still be a problem. When i give it gas there is a rattle that i can't place. I have been told it could be the flywheel but since i did leak antifreeze into the engine i have also been told it could be worn bearings. one more thing, it doesn't make the noise while i am neutral. Please give me some advice if you have heard this before or if you just know what it is.
thanks

[danny]

what is your oil pressure when in nuetral and in drive?

[78chevy]

my pressure is generally the same as before.

[89s10]

did you recheck the timing and what grade of gas are you runing the vacum advance

[danny]

if this happens only under acceleration then i would suspect the timing and fuel grade also.

[78chevy]

thanks for your tips and suggestions, they were well apreciated and i will see what i can do to get it running like a chevy should