This should be the easy part....

Putting in spark plugs after an engine swap. Went from a renix to a 97' HO, but kept all the wiring and sensors renix. I bought a set of plugs for the renix, but after reading a bit more Im wondering if I need the plugs for the HO head. Will the renix plugs work? Or should I take them back and get the ones for the HO head?
Thanks again,
Me

I just checked oreilly's website and it shows different part numbers for the two engine styles. I'd personally take them back and see if you can get a set of the champion truck plugs 412, I've got them in my 92 and 93 and no problems like the bosch +2 and +4 caused.

Go with the plugs for the HO. The renix head might have the plugs in a different position in the combustion chamber.

X2 - Match the plugs to the head.

Yep, get the correct plugs for the application.

Problems with the wrong plugs: if the "reach" is too short, you can get flame erosion of the exposed threads in the head; if the reach is too long, you can get flame erosion of the exposed threads of the plug and that will screw with the threads in the head when you try and change them. Also, you could end up with plugs that reach so far into the combustion chamber that there will be contact with the piston. And don't get me started on heat ranges--I really don't want to have to go there.

Renix uses projected tip, HO doesn't. Same reach.