I have an 86 TA with a TPI 350 in it that is running "370" casting heads. Straight plug over the counter replacements for a 69 Z/28 with the 302. 64cc chamber, pretty standard vale size, double hump with beehive springs. None of that is important though because I found out today, like an idiot, that those are likely flat mating surface heads that use an O ring! I have tapered header plugs instead, and I'm wondering if (because they seem to run fine) this would be a reason for low engine power output, and how soon I should replace them. Obviously I should do it, but with my headers, I have to put the car in the air to get to all 8 plugs. Right now I have accel 0576-4, and I would swap to accel 0437S (8199 to 8197).

My only other question might be, is the flat plug even a little shorter than the tapered plug, and is that possibly why its so hard to get them in and out with the headers on?

 

GM 3973370 SB Chevy Heads H-12-1969 1.94/1.50 Stock Camel Hump Over the Counter | eBay

If this is what you've got, they are nothing special.
Also these heads most likely are machined for both tapered seat and gasketed spark plugs.
Whatever plug you choose, you need to have the correct threaded length.
As far as headers and difficult to change plugs - that's normal.
Look here to make this job easier: https://www.thirdgen.org/forums/tech...ml#post6354844
The ACCEL shorty header plugs are the shortest you will find.