Has it actually been proven that the early heads are not suitable for unleaded. According to Dave at Puma Racing the early heads run fine on unleaded.

jiggaman:Ive got an 84 Orion thats never had a thing touched on the engine and thats been running unleaded for some time now, seems ok. Have a look at www.pumaracing.co.uk

alternatively if you decide you dont think its ok get an inline lead substitute thingy, they last for about 150,000 miles