Would ls1 heads fit on the lt1 block? and would the ls1 intake manifold fit on the lt1 block?

 

They won't fit. LT1 cylinder heads have reverse flow cooling while LS1 cylinder heads do not and the bolt patterns between both are very different. I would go with LT4 cylinder heads or aftermarket cylinder heads. If the cylinder heads won't fit, the intake manifold won't fit.

 

The only way they will fit is if you melt the LS1 heads down and recast them in the shape of the LT1 heads.