At this point I believe you need to put the wrenches down and start doing some research.

This is not a swap where you are installing an engine in the truck that was never intended to be there. Chevrolet made thousands of these trucks with small block V8s in them. This swap should be a bolt in. The key being getting the correct factory parts and mounting them properly. Spend some time on the internet and/or looking at actual trucks that have the V8s in them and see how the factory mounted them and with what parts.

As far as the throttle and clutch bracket I think you will find they are completely different between the 6 and 8 cyl trucks and your best bet will be to dig up the correct parts. I’m not sure if the bosses for the clutch bracket/ball are the same between the 305 and earlier SB engines and there is even the possibility that the V8 used a different bellhousing with the bosses located on it.......that is where your research comes in. Push come to shove you could always fabricate a custom bracket but that should be a lst resort.

Hoss is correct normally the transmission placement remains constant between the 6cyl and V8 models. If your engine now sits too far forward chances are you have the wrong mounts or have located them in the wrong location.

The factory spent a lot of time engineering mounts and brackets to make this body work with both Inline 6s and V8s. The problem comes when you try to re-invent the wheel. When you make a change in one area it will effect everything downstream from the change. It becomes a real domino effect ending up with a lot of fabrication and one off parts......and in my experience ending up with a cobbled together mess that never really works quite right.

I don’t mean for this to sound harsh but I’d like to see you avoid a lot of the common problems first time swappers often run into.