Well, if you value your ground clearance the transverse is the way to go. Since you have a '70 you won't need to run a converter so all you would have running under the car is piping which doesn't take up much space.
The only bad side of the transverse muffler setup is you are very limited as to the style of muffler you can use. With the standard dual exhaust, you can pretty much use whatever you want. I think the standard exhaust is the way to go if you're after performance, though.
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'69 Road Runner 440/4-Speed | '69 Road Runner 440/Auto
'76 Trans Am 462/Auto | '77 Trans Am W72 400/4-Speed
'78 Trans Am WS.6/W72 400/Auto | '78 Trans Am 455/Auto
'80 Trans Am WS.6 400/4-Speed
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