You are allowed one used component. This is usually the engine for emission reasons. Any engine can be used provided it meets the emission levels for the year of the engine. This is why a pre 1975 block is a good idea. Remember that the emissions at the IVA stay with the car forever and must be met at every MoT test.
IVA Emissions Years/Levels
Engine block date up to 31-7-1975 – no visible smoke
Engine block date 1-8-1975 to 31-7-1986 – no visible visual and less than (or equal to) 4.5 CO and 1200 HC at normal rpm hot idle. HC can be tested at 2,000rpm if Co passes at idle.
Engine block date 1-8-1986 to 31-7-1995 – no visible smoke and less than (or equal to) 3.5 CO and 1200 HC at normal rpm hot idle. HC can be tested at 2,000rpm if CO passes at idle.
Engine block date 1-8-1995 on
With oil temp at 60deg C, No visible smoke and at fast idle (2,500 -3,000rpm) less than (or equal to)
0.3% CO and 200 HC, Lambda 0.97 to 1.03.
At idle CO should be less than (or equal to) 0.5%. Catalytic convertors and fuel injection is mandatory.
Any headlight which will meet MoT requirements will be OK. Harnesses can be used. The height of the headrests will be checked. Steering columns need to be collapsible.
If using a Ford small block the date codes are as below.
The Ford casting number always starts with the 'Decade' character. Ford started using this structure in the late 50's with the first letter being 'B' . In the 60's the letter changed to 'C' and 'D' for the 70's and so on. The Decade digit is always followed by the 'Year' number. The combination of Decade and Year indicate the actual model year the part was originally designed for.
First character (a letter)
B= 50's C= 60's D= 70's E= 80's
Second character (a number)
Year of decade
e.g. C9is 1969
Third character
Car model,
A – full size Ford, D – Falcon, Maverick, E – Truck, L – Lincoln ,M – Mercury, O – Fairlane, Torino, S – Thunderbird, Z – Mustang, W - Cougar
Fourth character
Engineered component
E = engine
Cheers
Mike