what are the 2 holes in the floor just inside the bores? can the holes be blocked off?

 

They are EGR ports. Behind the "wall", a vacuume is present when air flows over, causing exaust gas to be sucked into the plenum.

 

They have something to do with the egr, I wouldn't block them off, why do you want to do that anyway?

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'88 RS (originally 2.8)
-350, .040 over, vette alum. L98s, stock tpi.
-305 injectors & chip
-TES headers & edelbrock cat back
-3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
on a 2.050 60 ft.
(Damn the 2.8!)

 

I see now why you want to do that!

 

I see now why you want to so that!