(1)Did you visually and measure the length difference on the pushrods?? We will start all over again here...(2)did your bike make a tapping noise prior you changing the head gasket...I don't believe I got a clear answer on that one yet...(3)did you swap out both head gaskets or just the rear head gasket?? If you swapped out both I most definetly would take the front down also...(4)are there any marks on top of your rear piston or valves from interference?? You stated none of the valves were bent how did you come about that determination?? Just visual?? Here is what I would do...never exceed any torque past what the manual tells you to...if I recall correctly torque proceedures are criss cross tighten until you have 15 ft LBS of torque then tightend one quarter turn more in the same sequence...BUT before you get that far I would disassemble the rear head check valve to guide clearence...lay the valve stem side on a table or flat surface and roll the valve with the valve face over the edge and get a visual to see if it is bent...if guides are no play and valves arent bent all should be good there that is if the valve isn't seized to the guide pushing up and down in the head...it does happen..inspect the valve shafts to see if there is any galling of them..galling will be pitted and scuffed real bad if they are that way I would install new ones and when you go do that buy the best that money can buy which is Kibble White Black Diamond valves...I wouldn't use anything else...if any guides are needed go bronze guides...you wanna do this once this will last a lifetime...install new teflon type seals not cheap scraper seals that the factory uses...hopefully we are past that part now...personally now if it were me we have a noise here in the valve train I would look into the pushrods for straightness lay them on a flat table and roll to see if they are bent, rockerbushings, rocker shafts, for wear..lifters, cam lobes, and cam bushings in the cover and cases...check all that stuff to see if there is any wear and for play side to side up and down on the cams...it is possible you have a collapsed lifter...check the lifter bore to see if the plungers are snug up under the retaining clip inside the lifter...check the roller on the lifter for up and down play...replace anything while you are inside the cam chest that doesn't look right...I've never ever heard of any head gasket on a hydraulic pre-loaded lifter motor being to thick that is non-sense...your gasket would have to be over 3/16 thick to even cause a problem....answer the questions I put before you and check the things I told you to...if you changed both head gaskets make sure you pull the front and check the same...you will find your problem...it is possible you had all the stuff cleaned and not lubed properly and threw it on...lifters could of bled down and you didn't pump them up first and collapsed a lifter at initial start by a short rev from trying to start it...any questions feel free to PM me or email me be glad to be any assistence...later Chaz