This is probably going to be one of those DUMB questions but here goes.
I have an l48 engine in a 78. It is rated at 185hp.  I have been looking at options to pump that up a bit.
One option is to use the existing engine and do some modifications.
Another is to just buy an engine already set-up for a bit more torque and hp and save the original engine in case I ever sell it (fat chance).
Anyway in looking at the crate motors I see 4 bolt mains and 2 bolt mains.
I believe the L48 in my 78 is a 2 bolt.
The big question for me is does 2 bolt or 4 bolt make any difference to matching it up to the transmission and fitting into the engine bay?  Basically since it has 2 bolt could I just pull it and drop a 4 bolt in, (well not me I still would want it to run).
Thanks for any and all info

No external difference.

And, ya never know - my 1979 L48 wound up being a 4 bolt block. Usually 2 bolts on an L48 but when they run short, whatever is next on the line will make do....

Thanks for the info, that explains it.
This group knows everything.
Thanks again

Things to consider when you are choosing an engine is to consider what you want to do with it and what's available for it.  Do you want the older style block and heads.  The block has the two piece rear main seal , the dipstick is on the driver's side and the heads have the valve cover bolts around the edge.  Or, do you want the newer style block with the one piece rear main seal and the dipstick on the passengers side with the heads that have the valve cover bolts through the top.  All of this is only a matter of preference.  Each of these engines has a plethora of parts available.  You could buy a short block so you do the build up the way you want it or you can buy a complete crate motor in either style.  You could also go to an LT1 or an LS series engine but those will take alot of additional engineering and electronics to complete the installation.  If you do opt for the later small block, your transmission dust shield (manual) or flexplate cover (automatic) will not fit because of the change in the rear of the oil pan that accomodates the one piece oil seal appliance. 

Thanks for the info - you're right lots to think about.
But thats half the fun with an older car - all the different options that are available , and then the endless discussions why we chose the one we did when its done.

[QUOTE=LukesVette]Usually 2 bolts on an L48 but when they run short, whatever is next on the line will make do.... [/QUOTE]

Personally I would save a chunk of money and have your original engine rebuilt... and beefed up to at least 300 HP... cheaper then buying a crate
engine... that way you still would have a matching numbers car (if you are into that stuff)...

After I blew the engine in my 72 (in the late 70's) I went the junk yard route and  purchased a 68'327 350 out of a wrecked Corvette  and put it in the 72...BEST THING I EVER DID...  the car is no longer matching numbers but I still think its a better car (read faster) after all these years...

Bob G.

I like then idea of keeping it original (sort of) but am not caught up in that.  That is the route I was sort of leaning toward.  I think it was criminal what GM did to the engines in those years especially in our vettes.