On the right hand side, in the back of the block there is a small embossment that has the engine number stamped. The 3 1/2 litre engine is easier than the 2 1/2 litre as you can use XK con rods (steel) as long as they are for 3.4 or 3.8 litre vesrion. The con rods for a 4.2 litre are too bulky and will not have enough clearance inside the block.
Cheers!
Ps. Here is my engine rebuild project thread:
Over here, where you can see a piece of yellow tape when I repainted the block:
You can also use the search function on this forum.
