difficulty timing engine

I have a motorhome with a 1990 Ford 460 with EFI. Engine is too tight at startup. Want to retard timing but unable to turn distributor after loosening the bolt for the securing bracket. I put a fair amount of twisting pressure but no success. Is this the way to adjust my timing or is there another way? There is no vaccume advance or points on this distributer. Also there does not appear to be a scale to shoot a timing light at, nor a lot of room. I was going to fine tune timing by ear.
Any advice?