Good stuff Bill. And yes, the bombs you have are American - sometimes used in late war by Lancasters, as 'extra' stock. But the Blenheim used the earlier British bombs, different in shape to those from late 1942 onwards, although they did have the cylindrical fairing around the elongated fins.
I think I have some 1/72nd scale 500 pounders, but they are the later type. I'll have a look in the spares boxes, as I might have some from an old Stirling kit, which were the correct type, as shown below.
Note that early bombs were originally painted pale yellow - until it was realised that bomb dumps stood out from the air in recce photos, when the colour was changed to dark green!
I've been wanting a 1/48th scale Blenheim, Mk1 or MkIV, but the Classic Airframes kits are going for silly prices on the 'bay' - the last one I 'watched' went for over £90 - plus shipping!!