If your bars are supposed to be 7/8″ it may have some 22 mm ones fitted. This sometimes causes things to be not tight, and the strip of beer can trick often works well. The strips under a twistgip need to well placed to not interfere with the twist bit.
I know Moto Guzzi and BMW have used 22 mm bars from the 1970’s at least, and I would guess at least some of the other European manufacturers did as well. The Japanese, surprisingly, used 7/8″ well into the 1990’s and may still do.
If your bike has 14 mm plugs, I have had good success with NGK B6EV. I would think any equivalent in that heat range would be ok. I have a 1949 600 Flying Squirrel. Brisk spark plugs from Czechoslovakia seem to be getting good reviews lately from people with oil burning bikes.