Vehicle in question is a 63 volvo l3303 4wd swedish military "tank hunter". PO pulled the b18 and replaced it with a fuel injected b20. Unfortunately he mismatched the b20 block with the original b18 head. PO also installed a weber down draft and header. So, from what i've been told that head/block combination will result in too much compression. True? Whenever I spend a lot of time in low gear 4wd oil spits out the breather cap on the valve cover. Other then that it runs fine. Want to run a compression test but not sure to use b18 or b20 compression standards. Thankyou in advance for any help.