I don't have the money, time, or space to rebuild the 350 in my 87 blazer. I do have a new 305 from an 83 chev. I'd like to just drop that in for now. I've heard some people say you can't do it because of the two piece rear main seal on the older engine, whereas the 87 used a one piece. Although others have said that you can just use the flywheel from the older engine without any problems. If anyone has gone through this or knows how to simplify this process, or what I'm going to need, it'd be great, thanks.  

The seal is not a issue is you use right flywheel and it will bolt in fine. The problem is the fuel system. Your 87 should be TBI and 83 is carb and if you put TBI on 305 it will need to some tweaking to get it right. Also if you have stock axle gearas and big tires you are going to feel it even more with 305 and that version of 305 is only about 140 HP too (87 305 TBI was 170)  

Thanks. The flywheel I have doesn't seem to have bolts holes for the torque converter. I only glanced at it quick though. Are there different flywheels for manual and automatic trannies?  This is also just a temporary job until I can get the 350 rebuilt. I'm thinking of just using the carb, that way I'm not changing alot of stuff around. Just hanging the tbi out of the way. Will the fuel pumps have to be changed? Would it be easier to keep the tbi or the carb? I'm also just running 35's on a two inch body lift. I'm waiting for the rebuilt engine before I go larger and get into tires, suspension, and gears. Thanks.  

You will need a pressure regulator to step fuel pressure down to about 6 PSI. You could try using a 305 Eprom in your current ECM and using TBI. A automatic uses a flew plate and a manual uses a flywheel. Flex plate should be same withe either seal type. ALso if you are running 35's you should have regeared long ago and I would do that before I would rebuild 350 as it will make truck run a LOT better. With some say 4.88's it would run better with 305 than it did with 350 and stock gears.  

I'm not sure if the gears are stock or not. I bought the truck from a guy a few years ago and don't remember asking if he changed out the gears. I'll know soon though as the rear pinion shaft oil seal is leaking and I'll have to tear into it. So the tbi runs at a higher pressure huh? What do the tbi's typically run at? thanks  

It is easy to figure out gear ratio without tearing it down and pinion leaks are easy to fix. YOu want to scrib a mark on pinion stub and nut BEFORE you remove nut to change seal and replace nut to exact same place to restore same preload. The TBI pump can be between 14 and 18 PSI and it is regulated to about 10 PSI at injectors. MPI/Vortec has a pump pressure of around 70 PSI.  

I've finally gotten some time off work to go look into a few things. I'm thinking of just swapping the 350's intake to the 305. That way I don't have to change anything with the fuel system and it'll be ready when the 350 eventually gets rebuilt. Also, how can I tell my gear ratio without tearing it all down? Thanks  

You are going to need to change Eprom in ECM for a 305 one because one will inject too much fuel. You will need to swap distributor as well and knock sensor. On gear ratio, simple jack up a front tire with hub engaged and count drive shaft rev's for one full turn of wheel and multiply the result by 2 and you have ratio. You can also find factory ratio code on inside glovebox lid in form of GU4, GU6,GT4 or GT5.  

Can you just purchase a new eprom or do you have to modify the one already in the truck? So I'd use the distributor and knock sensor from the 350?  

Just go to a bone yard and get a ECM out of a TBI 305 and pull Eprom out of it and put it in yours. There is a access panel on it for this as when you buy a new ECM is generally does not have Eprom in it and you use your old one. I recently scrapped out a car with a TBI 305 that I plan to rebuild and use one day.(for now it sits on a engine stand complete until I start overhaul) It pulled ECM from car too so I have Eprom for it.  

Great, now I just need to find a junk yard that's actually open on weekends when I can get to them. Maybe I'll be able to snag the knock sensor and a throttle positioning sensor while I'm at it. Does year matter on the 305 I get the eprom from? I've been trying to diagnose the old engine before I pull it. I finally had it idle-ing for the first time in awhile long enough to get it warmed up for a compression test. All the readings were high. Between 200 and 175. Seems like a big differnece to me between cylinders.  

I would shoot for a 87 to 89 305 TBI Eprom. As far as compression, I would not worry about your numbers as they look good to me. They are within about 10% which is fine. If you had a few that were 125 to 150 vs 200 on others I would be more concerned.