I have a 1981 Z-28 T-Top with the LG4 Engine, the LG4 is a smallblock V8 and produces 150hp. My question is this:
Is it possible to put a big block into the 81' frame? I want to add a big block to my 81 for the extra added horse power but I am unclear if I would have to do frame work before dropping in a bigblock.......

 

It's possible but a lot of hassle,much easier and less costly to build up a small block or buy a crate engine.
You can get plenty of power from an engine that will bolt right in so why hassle with a big block unless you just have to have one for bragging rights or plan on a super extreme machine that can only be built with a big (really big) cubic inch engine.
Even just a stock performance 350 would be a great upgrade and not break the bank.
You'll also need to start beefing up the rest of the car as you start making more power so you'll need to look at what you expect for hp and what your budget is before you decide on an engine upgrade.
Once you start passing around the 300hp mark it's time to start building the car to go with the extra power and that can get expensive.

 

Thanks for the reply.

After doing some research I think what I am going to do is just replace my 305 with a 350, hopefully I can find a 350 smallblock.......

 

Shouldn't be hard,probably more 350 Chevys were made than any other V-8 ever produced and more small block Chevys made overall that just about any other engine of any kind.

Here's about as much engine as you'll be able to get away with and not do a lot of mods to your car.
Just drop it in and go,everything is there carb to oil pan,no muss no fuss.

http://www.summitracing.com/parts/NAL-19201330/


GM Performance ZZ4 350 C.I.D. 350 HP Turn Key