I promised an update on this - so, after multiple events this year gettig oil heated quite high and driving car on r-comps, 2 DE events and 6 auto-x - I have 0 problems I had last year. Hydraulic valve lifters knocking is gone.

Oil was changed to 15w50 mix with 5w50 - 6qt 15w50 and 2q t5w50 as I had only one case of 15w50 in a garage. Workes fine so far. 50/50 mix could probably be OK too.