How difficult is it to replace a cam and lifters in a 69 gto 455?
I am pretty good mechanically, but I am by far not an expert. I would like to just take the engine out and send it to a machine shop and have the whole thing rebuilt, but I dont have those kind of funds.
Its not so much how difficult it is, the reply question to you is "Do you have a factory chassis manual to guide you in the removal & installation, do you have the correct tools, and IF you get yourself in trouble can you fix/repair the problem?"
I would suggest you first do much reading on how this is done. Then you might need to understand and have the tools to check your cam bearings to ensure they are not worn or out of round. No need to go any further with the installation as at that point the machine shop isn't an option - its a must. You might also want to check your lifter bores for wear and out of round - again, any problems here and its machine shop time.
Keep in mind that depending on what type of cam, ie duration & lift, you can get yourself into trouble with valve to piston clearances. You don't want a valve kissing the piston top. If you keep your lift stock, then less chance of any problems, and you can play around with the LSA and valve closing degrees. You also want to ensure you don't over cam your engine so you will need to know compression. Matching your cam to your drivetrain components is also a very important step in selecting an appropriate cam - and many overlook this and get disappointing results.
Selecting a cam that builds more dynamic compression will put more pressure to the ring seal, so your rings gotta' be good or you'll be getting additional blow-by or oil burning.
As you can see, many factors (and these are just a few to consider) have to be taken into consideration if you plan on doing a cam swap. Not saying you can't do it and not saying you will have any problems or issues, BUT, you should be aware of a few things that you could run up against and bite you in the butt.
Personal suggestion would be to forget about the cam swap at this time and save your hard earned money until you can properly do an engine rebuild and match all your new parts so everything works in harmony without any fears.