Declasse Sabre 550SS settings.
If you have Modloader then the Vehicles.ide, Handling.cfg, Carcols.dat and Carmods.dat settings can 
be simply installed by copying this file in a folder inside ModLoader directory.
Example: 
...GTA San Andreas\modloader\Declasse Sabre 550SS\Settings.txt

Replace the default line in Vehicles.ide with this one:
517, majestic, majestic, car, MAJESTIC, MAJESTC, null, poorfamily, 10, 0, 0, -1, 0.75, 0.75, 0

Replace the default line in Handling.cfg with this one:
MAJESTIC 1450.0 3100.0 1.5 0.0 0.1 -0.3 75 0.69 0.85 0.53 5 182.0 34.0 132.0 R P 3.6 0.52 0 30.0 0.4 0.13 0.0 -0.02 -0.15 0.5 0.3 0.10 0.56 35000 00552000 10000000 0 1 0

Remove the default line from car section of Carcols.dat and then add this line in car4 section of Carcols.dat:
majestic, 36,36,1,25, 31,31,1,25, 69,69,1,25, 92,36,1,25, 37,37,1,25, 54,54,1,25, 43,43,1,25, 97,97,1,25

Replace the default line in Carmods.dat with this one:
majestic, bntl_b_ov, bntl_b_sq, bnt_b_sc_p_l, bnt_b_sc_p_m, exh_b_m, exh_b_t, exh_b_ts, lgt_b_sspt, nto_b_l, nto_b_s, nto_b_tw, rf_b_sc_r, spl_b_bar_m, spl_b_mar_m, spl_b_bbr_m, wg_l_b_ssk

The vehicle name is defined inside Sabre.fxt. It's inside "Bonus\In-game name\cleo\cleo_text" folder of the archive.
That file must be installed in ...GTA San Andreas\cleo\cleo_text. You can do this by copying the cleo folder.