replaced headgasket, now wont start

allllright...so i recently replaced my headgasket on my 86 b2000 with a b2200 engine in it...i just took the head off the block and replaced it like that, put everything back together, and it wont start! ive tried to make the timing correct, but i think i might be doing something wrong. cuz it cranks, and itll backfire thru the carb now. like fuel will poof out the carb. so would it be 180 out? any info will help.really would like to get some cruises in this summer lol..

sound like the distributor is out 180 degrees or even off my a few teeth
did you make sure the timing marks were lined up?