[My427stang]

All toploaders - same case, same major internals except whats listed below (not counting gear ratios for wide/close ratio and length differences / tailshaft housing)

Small block and 390 FE toploaders - Small input and output shaft, but like I said above, gear sets are same as 427/428, other than in/out shaft (390 is same as small block box but slightly shorter input for FE, small block can be cut)

427/428 - Bigger input and output shaft, same case, same gear sets

Truck toploader - Think 3 speed with overdrive. Limited shifter options, wider ratio step. I havent messed with these but no-one is using them, that must be an indication

In a light Cobra, under 450 horse, I'd say the small block or 390 is plenty. If you are running slicks, go with a big input/output

Bottom line, aside from in/out shafts and overall lengths, all toploaders are the same, so there are no "internal differences" that make them stronger, just the input and output