I believe you are looking for a head from a 1972 Porsche 914 with a possible code or part number of 039101371A. There are some postings on a motor glider web site that discussed the correct heads for the Grob 109B that you should be able to locate if you Google this part number. The .pdf of the Grob 2500 engine IPC that I have doesn’t really state the number but there is a hand written part number and arrow to the head on the diagram in the IPC. From what I have read, there are also certain specifications for the correct valve seats as well. Hope this helps