Regards the screen, according to Gene Berg and others(check out the technical papers on his web site) he never built a performance engine with a screen left on the oil intake tube. He also does comment that full flow oil filtering is a requirement on all performance engines....
I had a problem with getting enough oil in my hydraulic valve engine when cold....when warm all was well. When cold I had a lifter that frequently would not pump up. Elimination of the screen immediately solved the problem.....
from GB's site, http://www.geneberg.com/article.php?ArticleID=237
"Oil strainer information. An area of extreme importance. The inlet or suction side of any pump is extremely limited in what it can do as compared to the pressure side and should never be impaired in anyway, whereas the pressure side is capable of overcoming a great deal of extra resistance. For that reason, I have not used the stock oil strainer in any of my high performance street or race engines since 1966. I found that it often caused too much restriction on the suction side of the oil pump with a little higher performance and high RPM engines. This problem was traced to oil starvation and all out bearing and/or crankshaft failures from the oil not being able to pass through the stock restrictive oil strainer screen fast enough to provide adequate flow to the pump."