904 lockup vs non lockup

A904 has ratios of 2.45-1.45-1.00 and is a non loc-up. whereas
A999 has ratios of 2.74-1.54-1.00 and is a lock-up trans.The
A998 should have the A999 ratios and should come without the loc-up.
That is my conclusion.
The higher the number the more HD the guts are..... from the factory. The loc-up TC is probably the weakest link tho. But it usually comes with a slightly higher stall. All are strong enough for your 318.
I have a 998 with a 2800Tc and a stock lo-compression long-block 1973 318. With a 4bbl,headers,dual 3" full length pipes,and 3.55s; she's a gem.... with 4.30s she was a ripper.