Hello,

I'm looking to swap the tired 305 in my 84 Trans AM for a 350 Vortec out of a 98 Silverado. The roller block in I'm thinking about installing is a one piece rear-main. Will that bolt up to my 84 700R4 Tranny or will I need to get some parts and/or modify anything to get it to fit? Thanks!

You'll need a 153-tooth flexplate for one-piece rear main seal, such as used in '86-up 3rd gen V8 auto. The truck is most likely 168-tooth, which may fit the tranny (most likely it's got the dual pattern converter mount pattern), but needs the 168-tooth starter which sits farther out from the engine and can interfere with 3rd gen exhaust.

Hehe It seems I've been talked out of rebuilding my 305 in favor of the 350.

I'm currently running Hooker 2055's which, when looking at it, seems to have quite a bit of room between the exhaust and starter.

For a $35 flexplate, I wouldn't risk it.

So just make sure I buy a 153 tooth flexplate and I'll be good then? Also, I was talking to a machineist and he said that sometimes with the one-piece rear main seal motors, something is different on the block that may not allow it to bolt up to my tranny...that true or will this thing line right up?

As long as it isn't the LSx style engine, you won't have any problems bolting up the tranny. A '98 won't be any problem at all.

Except I just remembered they often don't have the fuel pump mount drilled/machined, so you might have to install an electric fuel pump.

But that isn't a transmission problem.

Cool. It is not an LSx style engine...as far as I know. How would I tell the block's apart though I don't believe they put the LS motors in the trucks did they? Is there anything else I should be concerned about? From what I've read, just about everything is swappable...save my intake. I need to get one for the Vortec heads I'm putting on it. Only thing that could potentially be a problem that I see is I need to keep my emissions stuff so my intake needs to have an EGR provision...which GM makes. Other than that, is there anything else I should pay special attention to?

Ok...I'm going tomorrow to pick up the motor, it's a 350 4-bolt casting number 10243880. I wish I could go down to get the long block that I found for sale but that's another hundred miles to the south. Still, it has all the accessories on it and the rotating assembly...so I may pick both of them up...one for parts and one to use...hmm...

The 4-bolt block is According to the casting number not an LSX motor so if I get a 153-tooth flex plate, I should have no problems bolting it strait up to my tranny and starter. Will I have to get a new starter or will the one from my 305 work with the 153-tooth flexplate?


I'm going with World SPortsman II heads which will be modified for EGR.

I am going to try and find a stock rotating assembly (Crank and rods) and I would like to get some new Kieth Black Silvolite pistons to pull 9.1-1 or 9.3-1 compression. As this is a daily driver I need to be able to run 87 octane.

I've already got headers and a cat-back on the car now.

I'm keeping my Q-Jet and upgrading to an Edelbrock Performer intake (EGR)

Is there anything else I'm missing or that I haven't picked up on yet that I need? Thanks for any help!

You can use your 305 starter.

Why new crank & rods for a daily driver?

Because I'm building a 350 while I drive the T/A. If I parked the T/A then I could pull the motor and scavenge the Crank and Rods. In fact that would probably make sense wouldn't it? The crank and rods should be the same as I would get for a 350. Hmm...

Are you picking up an engine, shortblock, or bare block?

If it's an engine, it will have Vortec heads (are we still talking about the '98?). The crank and rods should be fine, unless it's for sale because of a wiped out bearing or something like that.

The guy who was selling the long block sold it about an hour before I told him I would buy it. Instead I wound up getting a 4-bolt bare block, casting number 10243880. It looks to be in good condition, no obvious cylinder damage and I couldn't find any visible cracks or the like. I'll take it to the shop tomorrow and have them clean, magnaflux etc. Then it's out of my hands. I'm just going to tell him what I want and let him do his magic.