Steve - Three kits to choose from would confuse me. How will you decide which is best for the SCW? I have the middle kit kicking around someplace in the stacks . . .
Apart from an obsessive interest in Panzer I's, a decent photo, and as there were only 4 Breda conversions? supposedly, there are some decent photos on the Web, a good reference book, and there are dozens, but in this case the Panzer tracts No. I-I, is excellent.
The photo starters
Shows the engine and air vent armoured cowls which are only in the Tristar kit, though you could replicate with foil and plasticard
shows some of the series 3 adjustments, wire cutters attached to the jack, rear nearside vision plate blocked off.
Larger glacis access plate with added lifting tab, and a Bosch horn.
All the above are listed on page 66, as features of the series 3 Pz IA.
The Tristar has 4 fuel filler caps, but as they are molded on, 2 can be filled and sanded off, to finish the conversion back to a series 3, as the 4 filler cap were a series 4 upgrade.
There are a few other bits to deal with, but you get the idea.
Time for some yard work as Storm Brian has battered the garden, perhaps some built time later today, hopefully