I think you will find that you will need the universal engine mount that is two separate legs which allows you to bring the engine all the way back to the firewall. My GP's P-51 has an OS 70 and this is the only way I could get the engine to fit. Since you mount the engine to complete the shaping of the plane's nose I imagine you could do some fabrication to extend the nose to allow for the added length created by the engine mount, but at $5.00 for a new mount I would save the work and try to keep the scale appearance. Just plug some round wooden dowel material into the holes in the firewall and drop some CA on them and your firewall will be as strong as new.