to start that's an engine code, not a block [casting] number - the first part should be all numbers, that is the I's are actually 1's, and it's a sequence number which all started at 1001, so yours is the 17,159th made - for the actual ID the F = Flint plant, the 55 = year, the M = 265 w/ HD clutch I believe if 55's were the same as 56/7 - is that what you think it is?
my thought is if it really is a 55 265, it doesn't have an oil filter or any provision for one, and the oil passage to the lifters goes thru the rear cam bearing, which can be problematic - good luck!
Bill
