i have the engine. It is a crate 540. However i need help. The vehicle is an 87 iroc z28 with the 305. 1. Do i need to tube out the front end? or can i stick with the unmodified body? 2. what motor mounts? 3. what transmission? 4. what rear? what else should i kno? thanks.

you didn't read the sticky, this is what it's there for. You don't need to tube out the front end. You can use the stock body. Your choice of intake manifold will determine if you can keep your stock hood.
Mounts. You can use the 305 mounts, but you should get EnergySuspension's poly inserts. Transmission: Sell yours before you explode it. You can adapt in a TH400. Or a 4L80E. You can get a TKO600. You can get a T56. That's about the extent of what will both fit and hold the torque.
Rear: Again, sell yours before you explode it. You'll need to either get a 12-bolt from moser or Strange, or a Ford 9" from Currie or someplace.

I'll also add that Strange offers their S-60 rear, which is based on the Dana 60. And if you want a 700R-4 or 200-4R, these can be built up to hold up to 620 ft-lbs. Just how wild is your 540, anyway? You could get TCI's new 6-speed automatic, and be the first to install it. We'd love to see that.