I have a T Bucket with an almost stock 1978 305.  It has only an aluminum 4bbl intake and headers.  I've got bubbles in the radiator and water comes out the water inlet on the intake.  What have I got?  Cracked head, cracked block or ?????   Could it be an intake manifold leak?  I replaced the 3x2's it had with the Edelbrock 4bbl intake last winter but I drive it so rarely that I can't really associate the problem with the manifold change.  Tks in advance for your help.

TeeBkt  

You must first start with the basics. Is the thermostat functioning properly? Is the radiator clogged restricting flow? Are the fins deteriorated in the water pump causing insufficient flow? What kind of condition is the radiator fan in? If all checks well you may have a blown cylinder head gasket. It is usually easiest to start with the thermostat.
The thermostat can be checked by boiling a pot of water and carefully placing the t-stat inside to check its opening characteristics.  

Agree with Dan, always best to start with the basics and most obvious first.

With bubbles in your radiator, I'd say that means the system is getting air pumped into it, probably from a bad head gasket or cracked head. Those late 70s small block heads were notorious for being thin castings and not very good. One decent overheat and you were sure to have some cracks.  

if you can remove the fan belts and find a tapered plug with a center hole in it and some clear vinal hose  you can squeese the upper hose with the end of the clear vinal hose in a container of water to fill it even more..

start the motor and see how fast the cooling system coolant expands..  dont run it more than 2 minutes without any circulation.. ..please...

professional techs are removing the pressure transducers from removed gas sending units on OBDII cars and wiring it to their digital storage scope or graphing multimeter and watch the tiny pulses that a blown head gasket will produce in the cooling system... this has to be done with the water pump not turning... so every motor type cannot be tested... a few bucks in a cork and some clear hose will do for most diagnostic work....rubber corks a like this are sometimes available at hardware centers...


oh yea.. if you do get a pulse you start killing spark til the pulse reduces.. this points out which cylinder is causing the problem...

if you have a compression tester that the quick disconnect end fits your shop air hose.. you can take the valve core out.. and using a remote starter switch.. bump the motor over til you get that piston to the top of the compression stroke..  and then clear you hands out of anything that can turn..  and pressurize that one with shop air.. all while watching the level in that same vinal hose...