Your not going to blow up the 7.5 any time soon so why rush. Why not keep looking and wait for a 8.5 to pop up. Or do the upgrades and for sure an 8.5 will appear making you ask yourself, w the f did I do...
Gonzo, your combination will be fine. Similar to mine, in fact. My 305 is factory stock with the exception of an L82 intake, which I suspect is just an aluminum version of the stock cast iron intake.
I put my 7.5 together with junkyard parts using a 3.42 gearset from an S10 and a 26 spline posi carrier from an 87(?) Camaro so that I could reuse my original axles.
My 200-4R is essentially stock with a rebuilt 2200 converter. It was pulled from a well maintained '90 Caprice wagon.
I used a gear calculator to determine that my 3.42 were the overdrive equivalent to my stock 2.29s with my TH200 so my cruise RPM and mileage stayed exactly the same.
I mostly drive my car like an old man but occasionally beat on it and it's been to the dragstrip a couple times. Held up fine with this combo for several years but I've got changes in the works that will require a beefier rearend and some transmission upgrades.
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