1978 F250 coolant leak

I have a 1978 F250 4x4 with the following on the engine ID tag: Engine family 351M/400, displacement 400ci. It has the 4 speed transmission installed and the engine runs great. The problem is there is a leak of coolant coming from the bottom of the bellhousing. I've tried Alumaseal twice, then some kind of "permanent" copper engine block sealer and these products have not worked. I'm thinking that I may have a bad freeze plug or two at the back of the block or the heads, but I am not very familiar with these engines. Are there freeze plugs at the back of the block? If that is the problem, would it be easier to pull the transmission and transfer case (yikes!) and work from the back / underside or remove the engine and replace them while on the cherry picker? I guess while I'm there, it would be a good time to inspect / replace the clutch, Etc. I'm disappointed the sealers didn't work, I'm not looking forward to the job.

TIA,
Dale

It'll probably be easier to unbolt your exhaust manifolds, drain some coolant, remove your intake, and just pull the heads off. Then you can change all the freeze plugs plus install new intake gaskets, and you should be good to go......

I just checked the back of the head on the passenger's side (I can't easily see behind the driver's side, the power brake booster is in the way), no freeze plugs or any sign of a coolant leak. It appears to be coming from the "weep hole" at the bottom of the bellhousing.

I just checked the back of the head on the passenger's side (I can't easily see behind the driver's side, the power brake booster is in the way), no freeze plugs or any sign of a coolant leak. It appears to be coming from the "weep hole" at the bottom of the bellhousing.
This might sound crazy, but go to the GM dealer and get the pellets for the radiator, they come in a blister pack. This stuff is amazing!! Trust me this stuff really works. Sorry, can't remember the name of it..mike..

Just real quick....does that have a removeable dust shield right underneath the clutch?....You may be able to see up in front of the flywheel and have a peek at the block. I know most V8's have oil plugs on the lifter valley right in the center of the rear of the block, but for the life of me I can't picture in my head where the freeze plugs are......You hold on...I'm gonna investigate...