I've got a 1979 F250 w/460, c-6 trans, How big of deal is it to replace the rear main seal with the engine in the vehicle?

 

Get a hoist...Take the radiator out and fan off...Unhook the exhaust..Unbolt the motor mounts...The drive shaft...Anything else needed to get the engine off the mounts... Drop both transmission crossmembers and lift the engine off the mounts enough to get the oil pan off..Drop the number five main and replace the seal...

Metro2

 

 

...in other words... Piece o' Cake!