Confucious say, man with most money go fastest.
LT1 heads vs LS1 heads, no comparison. LS1 heads will outflow LT1 heads hands down, ported or unported versions of either, when comparing amount of money spent. A mild cam with a stock LS1 motor can put down well over 350 RWHP. LT1's would be lucky to break 300.
But you can't put a pair of SB2.2 heads on an LS1 block, but they can be made to work on an LT1 block. So if you're willing to drop the money, you can make mo' power. This ignores the C5R aspect 
but we probably aren't talking about $6k blocks and $3k bare heads on a Fiero forum. 
If you're running a factory computer, the LT1 won't rev above 7000 RPMs (computer cuts off). LS1's can do it no prob (my shift point is 7200, have gone as high as 7500).
Properly built, the motors will likely cost about the same. If *I* were looking to do a retrofit, I'd do an LS1 based on the weight alone. The computer system will be more expensive with an LS1, but I think the advancement is worth it. If the LS1 intake is 'too ugly', you could always get a set of 'vette Fuel Rail Covers (FRC's), or even get a LS1 Holden (Australian version) plenum cover.
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85 GT 2.8/Auto (in progress)
2 x 86SE 2.8/Auto (parts cars)
79Z28 / 94Z28 / 98Z28
1 wife who thinks I'm nuts...
