Hey there!
I apologize if this information is already readily found or posted, but I had the good fortune of buying my first truck this weekend and I'm stoked on it. I purchased a 1987 Chevrolet K5 Blazer with a 305 (I believe it's TBI) and an SM465 Muncie 4-speed with granny low. First off, I love the truck and it runs and drives completely fine. However, the previous owner put a 4in lift and 35" tires on it and geared it super low, and as fun as it is, it's just not feasible to drive to camping spots or 4x4 locations on the highway. I don't know too much about this stuff yet as I was hoping to learn on this bad boy.

I had been researching ways to get my 305 a little upgraded and better suited for some highway driving and everyone's advice is generally, "don't waste money on that 305. Run it into the ground and swap it with a 350". Which, I guess I'm fine with, but gives me a slew of way more questions.

Can I relatively easily swap out my 305 with a 350? Which 350 specifically (after some cursory research, there are a ton!) and would it work with my existing transmission. Having to replace that too would make this cost prohibitive, as I'd rather save up a lot more money and do an LS swap if I have to do the whole thing.

Has anyone swapped this particular swap before, or this truck, or this motor with the same transmission?

 

Yes, 305-350.

 

Well yes I'm aware it's a possible swap, my question more pertains to which 350 I should be looking at since there were so many made, and if it would port to my existing SM465 transmission or would require me to get a new one, which would make it cost prohibitive for me.

 

I don't think you will even have to swap bell housing. You might research bolt pattern for what you have to what you want to swap. That's the only thing that might be different. Small block flywheel same as a small block, since you have a manual transmission I don't see an issue.

 

what do you plan on accomplishing with the 350? this isnt going to fix your rpm issue. my understanding with you post is when you say its geared super low, is that youre saying it has something 3.23 gears and you cant really take off???. if this is the case i dont think a 350 will fix your issue and you might be better off with an axle swap
or are you saying it has something 4.56 and your top speed is pretty much around 60 mph? again i dont think a engine swap will help you. if youre looking for more grunt then ok, but you still wont have the proper rpms
start with finding your rear ratio and go from there. the sm465 is a good heavy duty trans but its no race trans and the 1:1 final ratio tends to leave a lot to be desired.
How to determine what ratio you have without removing the cover

on a side note my 79 has a 350 sm465/np205 with 4.10 and 38s. i could go 70 mph no issue but if i drove conservatively and kept it under 60 i could see 10 mpg