What is the difference between early 70 and late 70-72 ignition shielding on sb corvettes? I am looking for some driver quality pcs and some stuff on ebay mentions to ensure it fits your application. Are any parts interchangeable? I read something about motor mount changes in 70, is it just the horizontal shielding that is different?

 

Mines a 73, and never had one when I got it. 2 supports are there but Chrome top is not. Honestly I havnt seen a reason it's needed. I drive all year long never had an issue. Would love to know it's purpose. I know, a shield, but what's it shield? Just seems like decoration to me.

 

There are a few purposes.
Shield over distributor was to help with interference with radio. Also I let the ascetics it provides.
The side shields provide a clean look as well to hide plug wires.
The shields at the plugs is to help with heat at the plug/wire.
There are spark plug heat shields (U shielding) that allows you to run the wires between the block and exhaust manifold.

 

The early 1970's 350 engine had 2 significant difference from your car; 2 piece distributor box and chrome shields on L & R front 2 plugs. I have a 70 that is right at the time changes were made as I have a 2 piece distributor box and only rear chrome plug shields.
So, late 70-72 should have a one piece chrome distributor box and horizontal chrome shields on the rear plugs.

 

The "early" 70 350 came with the 4 lower shielding pieces to cover all four pairs of spark plugs, while all later 70's and 71-72's only got lower shielding on the 2 rear pair of plugs. The 70-79 left rear plug cover can be identified by the large hole stamped in it to clear the TCS switch in the right hand head, that wasn't present in the 68-69 right rear cover. 68-70 early all use the same left rear shield.

The top shield over the distributor on early 70's was the same 2 piece cover used in 68-69, consisting of a four sided open box and a separate lid, held together by 3 wing nuts. Late 70's through 74 used a simpler, one piece top cover. The same top supports were used with both the one and two piece top shielding covers.

All 68 to 77's used the same left and right rear vertical shields, that cover the wires where the run up behind the block, from the rear lower covers to the top cover.

 

So since my TPS has long been removed, technically I could run the early 70 shielding? If I find something that has the 1 pc dizzy cover ( I like that look ), then the other details are small for a car that isn't getting judged. What about the 73-74 shielding? Is there any significant differences on those?

 

All 70's used the lower right rear shield with the TCS hole. If you want a right rear shield without the hole you'll need to find a 68-69 one.

73 and 74's used the same one piece top cover as the late 70 and 71-72's, as well as the same top cover supports and left and right rear vertical covers. The same right rear lower cover with the TCS hole is used on all 70-79 Corvettes, including the 73-74. The left rear lower changed slightly in 73. The stamping was changed a little on one side of it, but the overall appearance remained the same when installed. The new 73 left lower cover was used through 79.

75-77 Corvettes got a new, larger one piece top cover and new supports, to cover the larger cap the HEI distributor used. The same verticals and rear lower covers as the 73-74's, continued on for 75-77.

In 78 the chrome top cover and two vertical shields were replaced with a black, molded plastic, one piece cover, but they still used the same two rear lower covers as the 73-77's. The black plastic cover was used through 82, though one side of it was shortened for 82 to clear something associated with the CrossFire injection.

To go back to your original question, the change during the 70 model year was the switch from the two piece top cover to the one piece, and the elimination of the left and right lower front plug shields. Everything else, the verticals, all the supports and the two rear lower shields, remained unchanged between the early (first design) 70 shielding, and the late (second design) 70-72 shielding.