I have a typical ID question that I am hoping you guys can shed some light on. I have a 355 short block that I was going to put into my 80 El Camino but decided to hold off on the 355 since I want to build it right with nice heads and a nice cam and I just dont have the money to do that. Instead I want to buy a basic used 350, freshen it up and drop it in with my new TH350 trans. The car is a daily driver and I am looking to get a basic 350-370 HP motor to drop in to pull a 2,000 lb trailer behind this car.

Anyways, a buddy of mine has a 350 he pulled from a 79 Camaro that he wrecked (not the original motor keep in mind). Miles are unknown but he is going to let me pull the heads to make sure I want it (it ran fine and had new valve seals and such put in about a year ago or more and I drove and rode in the car with this engine). The numbers I pulled from the back of the block are the typical 3970010. Front of the block I have 151209794 K05 30 CMJ. I understand that the number after the 5 should be a letter, my guess is it's an L or i, I can't tell. Here is what I was able to I.D....
K= St. Catherines, Ontario (McKinnon Industries Canada).
05=May
30= 30th day
CMJ shows that it's a 1974 350 4 bolt main from a full size car with a T400 Police trans).
If it's a 74 block then why would the 5 in the above number show as 75?

Here is the sites/links I pulled the info off of: http://www.nastyz28.com/gm-chevy-cod...s-suffix-2.php

http://www.nastyz28.com/sbchevy/sblock.php

My question is, what year is the block. 74 or 75? Are there differences with the Canadian blocks and heads compared to US? Better or worse?
As for the 4 bolt mains or not, I could care less if it's 2 or 4 just because the fact it's a street car and I do not plan to go over 370 HP (most likely will end up at 350 HP tops because of money issues).
I am sorry for all the questions and rambling on, I am just trying to provide as much info as possible. Thanks a lot in advance!