ENGINE NO.
PREFIX   ENGINE SIZE    CAR
G        948cc          Herald 948
Y        948cc          Herald 948
GA       1147cc         Herald 1200
GD       1147cc         Herald 1200, Herald 12/50
FC       1147cc         Spitfire I,II
GE       1296cc         Herald 13/60 (Early)
GK       1296cc         Herald 13/60 (Late)
FD       1296cc         Spitfire III
FH       1296cc         Spitfire IV
FM       1493cc         Spitfire 1500
HB       1596cc         Vitesse 6
HC       1998cc         Vitesse 2 litre (I, II)
KC       1996cc         GT6 I, II
KE       1998cc         GT6 III
DG       1296cc         1300 Toledo
DH       1296cc         1300 Dolomite
RD       1296cc         1300 Front Wheel Drive
RF       1296cc         1300 Front Wheel Drive
WB       1493cc         1500 Front Wheel Drive
YC       1493cc         1500 Rear Drive Dolomite
FP       1493cc         MG Midget
MB       1998cc         2000 Mk I
ME       1998cc         2000 Mk II
ML       1998cc         2000 Mk II
CP       2498cc         TR5 very early TR6
CR       2498cc         MKI 2.5PI Saloon, Estate (132 bhp good engine!)or Late TR6 (125bhp not so good engine)
MG       2498cc         MkII 2.5 Pi Saloon, Estate
MM       2498cc         2.5 TC Saloon, Estate
MN       2498cc         2500S, Estate


Gear Ratios
	1st	2nd	3rd	Top
	3.5	2.16	1.39	1	Standard ratios	
	2.64	1.78	1.25	1	GT6 ratios (bit tall in 1st for 4 cyl)	
	3.11	1.93	1.31	1	Alternative ratios (Marina/Ital - recommended for 4 cyl)	

Different Differentials

There are a number of ways of identifying a differential - either by counting the crownwheel teeth and dividing by the number of pinion teeth (eg c/wheel 35 pinion 9 = 35 / 9 = 3.89), or by counting the number of turns the front flange requires to turn both output flanges by 360 degrees (or one output flange by 720 degrees) - just more than 3.6 means 3.63, just more than 4 means 4.11.

By just looking at a differential, you can often narrow down the ratio. For convienience, we often split differentials into 4 types:
    Type A Square front pinion flange. 5/16 bolt holes all round (1/2 AF spanner size). Small quarter shaft diameter inside. Casing no's G, Y, GA, FC to 120,000.
    Type B Square front pinion flange. 5/16 bolt holes all round (1/2 AF spanner size). Big quarter shaft diameter inside. Casing no's GE, FC from 120,001.
    Type C Square front pinion flange. 5/16 bolt holes on front flange (1/2 AF spanner size). 3/8 bolt holes on ourput flanges (9/16 AF spanner size). Casing no HB.
    Type D Round front pinion flange. 3/8 bolt holes all round (9/16 AF spanner size). Casing no's FH, FK, FR, FD, HC, KC, KD.
Type A and B are indistinguishable from the outside, but Type A shouldn't be fitted to a 13/60 as the quarter shafts are liable to break. Type C (which was only used for the Vitesse 6 originally) is very prone to quarter shaft failiure.

Having decided which differential you have, you may now wish to alter the ratio. The following table gives rounded figures for miles/kilometersper 1000 rpm.

Diffy In top at 1000rpm		With overdrive
Ratio		MPH		KPH		MPH		KPH
4.875		13.50		21.50		17.00		27.00
4.55		14.50		23.00		18.00		29.00
4.11		16.00		25.50		20.00		32.00
3.89		17.00		27.00		21.00		33.50
3.63		18.00		29.00		22.50		36.00
3.27		20.00		32.00		25.00		40.00


Universals

GKN UNIVERSAL JOINT 18179
GKN UNIVERSAL JOINT 18050
GKN UNIVERSAL JOINT HS151-1


http://www.triumphspitfire.com/enginenumbers.html
http://www.canleyclassics.com/?xhtml=xhtml/product/swingspring.html&xsl=product.xsl
https://shop.tssc.org.uk/category/gearbox-and-drive-train