They are way down on power due to retarded timing, cats, big port heads, smog crap, etc... Also, the blocks are weaker due to metal being taken out to save weight.
it mostlt depends on what head castings you have. some of the 75's had the D0OE heads early in the year which are about the best stock windsor heads, however if they are D5OE castings they suck ass, small valves thermactor passages drilled large chambers so they are low compression smog heads. the block is a decent unit, but an earlier block is preferable, still really not that big of a deal. the worst thing is the reverse dome pistons, with the big chamber heads the comprssion is really low about 8.5:1 if i remember right.
if you plan on rebuilding it and have the better heads it should be a good engine for you. even if it doesn'ty the better haeds you can buy the roush windsor cast iron heads for about 700 bucks or you can get a set of CNC ported earlier castings with 1.94/1.60 valves and screw in studs and guide plates from www.powerheads.com for about the same price