The problem then being you have also lost the break-in surface that every new cam has until the parts bed in to each other. Once they bed in and are matched much less of a chance of wiping lobes off. Cams are often thinly surface hardened to allow for the first break-in. What the dark gray or black coating (parkerizing) does too.
Depends on how worn the rockers are, if they have anything other than very soft polish wear, like lined wear or flats or angles then you will have a problem. Honda uses very cheap surface hardening that is not very thick, wear through that to have visible wear marks and you are now on soft steel that if meeting the same surface as before can still live a while but dies like a dog if mismatched to get oddball running meet-up surfaces. You can measure cam lobe highs too to tell any relative difference in lobe height, anything more than .005" lobe height variance and that lobe is getting seriously worn and likely to go when forcing a second break-in. Note that the exhaust lobes can be a different height from the intakes, normal that. You are looking for differentiation in the intakes or exhausts as a set. Also look at the highest loaded part of the lobe, the tip, any with pitting and you will have trouble, the lobe is already going. Light pitting is usually OK on other parts of the lobe but on the tip is death.
I've pulled it off on a lightly worn motor but you avoid it if at all possible. I take #600 sandpaper to the rocker wear and cam lobe surfaces in a moving around pattern to both sand off any erratic highs as well as leave a surface that can break in easy but won't work if the wear is too hard there. On the big lift race car engines we would assemble not using all the spring required, just one each valve and do not rev the motor high at all, do the break-in and then put the other springs back on. About the only way you can get huge lift flat tappet cam lobes to live longer than a few minutes but a real pain in the butt. Thank God for roller cams.
For sure if you try making the parts work, make sure you use a good brand cam break-in lube, often it makes the difference in good running parts and junk. Break in the cam then you change the oil and filter to go to what you will normally run. The lube MUST have a good amount of moly (molybdenum) in it.
More death in pistons/rings, they are matched to their running cylinders, not having that the engine will often run like crap too but rarely you can get away with it. Rods are marked as to position but if completely disassembled you lost that, the pistons then are lost as to hole. Each different piston/rod assembly is slightly different in length to make the rings run in different locations up and down, a ring even so much as kissing the end of ring travel from too long and that ring breaks easy as spit. Mismatch the rings and they are forced to re-break-in but the wear provision for that is already gone, great way to make a smoker. Rings can only break-in one time, past that and they pretty much go back in the same hole with same rod and piston to easily fall back into the same slow wear pattern they had before. I don't even like to disturb pistons/rings in a block at all unless I'm forced. Pulling a cylinder block always exposes you to the random chaosian factor, dents and dings in parts can come from anywhere, on rings it's death. If I pull a block I commonly dress the cylinder walls again with the #600 sandpaper just to give some 'new' for the ring to lightly have to again wear through, it works pretty well. Or hone if new rings going in.
If your parts wear is too hard or pronounced there really is nothing you can do, you will have trouble. X2 on the people who say they 'have done it', if I ever saw the result of it the motor was a dog but many think that is good.
On the 16V DOHCs I work on I use 16 separate heavy duty quart freezer bags to keep all head parts organized in and more if needed on other, a freaking puzzle but what you gotta do. Mismatch even the separate cam caps on those and tear the motor up in 5 minutes.
