Dont know if this will help, since its a crate engine you may not have the zddp issue to deal with, but I just got this off the Mobil 1 site, since I use Mobil 1 in my 440:
Question:
Mixing Motor Oil to Reach the Right ZDDP Level for Classic Cars
For an older, flat tappet, performance motor with inherent cam wear issues is there any benefit to mixing high ZDDP Mobil 1 Racing 4T 10W-40 to Mobil 1 High Mileage 0W-30 oil? The 15W-50 creates TOO MUCH oil pressure. It would be nice if you had a product for 'Classic' cars, high ZDDP, 0W-30 and 0W-40. I have used nothing but Mobil 1 for 15+ years.
-- Bill McCauley, Tallmadge, OH
Answer:
Mobil 1 0W-40 already contains a higher level of ZDDP (1000 ppm) that could benefit your flat tappet engine. We also have a Mobil 1 High Mileage 10W-40 (1000 ppm); see our table listing the phosphorous levels for all Mobil 1 motor oils.