Cylinder heads are a complicated and simple at the same time!
All 1300 and 1500 heads are interchangeable in that they will all bolt on, and all manifolds fit as the inlet/exhaust port arrangement is always the same. However it is vital to get the compression ratio correct for the fuel available.
|515573 13/60 Herald||small inlet valve||figure 8 valve retainers||8.5:1|
|515973 Spit Mk3||small inlet valve||twin collet retainers||9:1|
|218139 1500 forward||biggest inlet valve||8:1 (on 1500)|
|218140 1500 forward||biggest inlet valve||9:1|
|218141 1300 Toledo||big valves||8.5:1|
|218142 1300 Spitfire IV(not US market)||big valves||9:1|
|TKC1156 Dolomite 1300||slightly smaller inlet valves||no water outlet in RH rear corner||8.5:1|
|TKC1155 Spitfire/Dolomite/Midget 1500 (not US market)||slightly smaller inlet valves||9:1 on 1500|
|There is a variety of USA heads with/without valve seat inserts, with/without air injection, and some at 7.5:1 with dished pistons or 9:1 (1976) with flat. Physically they will all bolt on.|
Problems occur with 1300 heads on 1500 engines as the compression is too high, but a 1300 head at 8.5:1 is fine with the 1500 dished pistons (low compression pistions)! Torque of an engine is really related to its capacity, the BHP can be increased by making the gasses get in and out easier and faster but this is always at the top end. The most important thing normally is to get what is there working correctly.