javsst70

1994 X-Cab 4x4 Pickup. 153K miles. My wife has owned since new. First HG was done under warranty. Second was about 11 years and 40K ago on Cyl. 5. About 2007, the water pipe under the manifold sprung a leak from years of green coolant - lots of sludge. Now it has gone on #5 again. Both times I have seen the failure, there was no milkshake, most of it burned up or came out on the side over the starter. Of course, I just did the timing belt and water pump a few months ago.
I met my wife in 2001. I didn't get into the Toyota specific maintenance until a few years ago, when we decided to fix it up for our now 17 y.o.. I have rebuilt a 1970 AMC Javelin and done plenty of work on domestic cars, this was my first Toyota. Thanks to a guy hitting us, we had it repainted with the insurance $.
What I am wondering is whether I need to get a different head for the right bank of cylinders? Don't know if there is a weak spot somewhere that keeps failing or if it is the heat from the exhaust. Also, since it has sludged up badly in the past, should I plan on going thru the block as well?
Yes, I know, swap a 3.4 - not an option. Just want it to run for a while.