-Many factors affect the location of the motor in a street rod chassis. Plan ahead.

-The frame should be at ride height and rake when mounting the motor/trans.

-On MII suspended chassis, have the rack mounted. It is usually higher than the crossmember and can interfere with the oil pan.

-Get Inline Empire Driveline tech sheet re driveline angles. ( http://www.iedls.com/ptsetup.html)

-Carb does not have to be level, but try to be close.

-Pinion angle (up at the front) should be the same as the crank/trans angle (down at the rear) and the u-joint angle should be 3 degrees or less.

-Crank c/l does not have to be in line with the pinion when viewed from above.

-Crank/transmission line does not have to parallel with the frame c/l when viewed from above. e.g. The transmission is in the center of the 

frame (located because of the stock x-member passage) and the front of the motor is offset to one side (usually the passenger) for clearance. 
The 3 degree u-joint angle is the determining factor, as above. (Per Inland Empire Driveline/Armando)

-Have motor/trans to know the clearances required.

-Have the rad mounted. It often can be moved, but sometimes must be in a specific location (and sometimes on an angle).

-Know what fan will be used so clearance can be planned.

-Have the body mounted.

-Have the firewall or be prepared to custom make it.

-The floor might have to be modified for trans clearance.

-Headers & steering will want the same space. Consider this when positioning the motor.

-Rubber OEM mounts absorb more engine vibrations than urethane 4-bar bushings. The urethane 4-link bushing mounts usually look more "high-tech". Use the mounts that suit the style of your project rather than worrying about the amount of vibration transfer. It won’t be that much different.

-Plan hood clearance.

-Have the water pump installed so clearance can be planned.

Welder Series has many nice bracket and kits. Check out their websire for details on all of their parts.