Oil + additive viscosity

Billbo I don't know if your engine is a new build as I wouldn't recommend putting synthetic in unless you have some miles on it. have you tried the Penrite 15-50 ten tenths full syn ?. I use this in mine as I use the 10-30 as well solid flat tappet.
https://penriteoil.com.au/assets/pis_pdfs/10 TENTHS RACING 15W-50 (100percent PAO & ESTER).pdf