A 135 is usually adequate for 4x5 specially small prints, but it is really for 3 1/4 x 4 1/4. 150 is better but requires more column height.

Omega C are for 6x7 negs. To my knowledge there is no C 4x5. D models are 4x5.

You need a 4x5 condenser set which is 6 1/4 " diameter or if a diffusion enlarger, a box that covers 4x5.

You may need longer cones for some D models, 3 1/4 or 6 " if all you have are 3 or 4" bellows like a D2.