'89 valve guide seals questions

Hey guys, I'm quite sure my valve guide seals are leaking in my new truck, and I'm just looking for some answers. When I bought it it had filthy oil that hadn't been changed in a lone time, the po hadn't changed the oil since he bought it 1 1/2 years ago, even though it sat for 10 months it neededs a couple oil changes to get some of the dirty oil out. I came across 12L of free 5w-30 so with it being just below 0degrees Celsius here I put it it. Now on start up I get quite a lot of blue smoke but it goes away after running for a bit then no longer smokes. I know when I do my next oil change and put 10w-40 the problem will become much better but now I know that they are leaking some. I'm thinking of replacing them but a couple questions have come to mind, how easy and what tools do I need to do it without removing the cyl head? I'm worried as soon as I pull it off it will warp. How much do cyl heads run for? And possibility of putting in a rebuilt engine, how much and where's the best place to find one?

You can change the seals with the head still inside. You can rent the tool at a parts house, just get the camshaft out, and do it one cylinder at a time. The other important point is to either use compressed air or string into the cylinder being worked on. Also a great time to replace camshaft seal