You will need to get an assigned number for the '54 in the state of Texas.

Your '54 was originally titled by engine number. Chapter 25 I of the TxDOT Motor Vehicle Title Manual states:

Quote
If a new or different motor has been installed in a motor vehicle which records the motor number as the identifying number (all 1955 and prior model motor vehicles, except Ford products manufactured since March 31, 1932), a corrected title application must be filed. The method of filing an application to correct a certificate of title as a result of a reconstructed(sic) is the same as discussed in par.II of this section.
It also goes on to say if a motor without a motor number, such as the chevy motor you want to install, is installed in a vehicle which requires a motor number, an assigned number must be obtained from the department. (refer to chapter 13)

I'm not going to type it all here. What you need to do is go to your local tag office and get all the required forms.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.