i went with iran travelling centre as the agent for my iran visa see link
for the pak visa i am pretty sure you will need a letter of intro / recommendation from your own embassy, probably cost about 30 USD.
provided you have the MFA number from the iranian agency, and the loi from your own embassy, both the pak and iranian visas should be obtainable in delhi. you have to go to each embassy, pick up bank account details, deposit the fees into their bank accounts etc. and generally waste time running around getting photos they are happy with etc. no big deal but expect to spend 3-5 days in delhi.
i think you will have the most trouble getting a carnet for your enfields. there is a link somewhere on hubb for the indian automobile agency and info on getting a carnet for an indian bike. i vaguely recall the link saying this is particularly difficult or painful.
i went thru india-pak-iran-turkey from 30 jan - 7 mar '10 and generally had a great time. i had escorts most of the time from sukkur-quetta-taftan-bam (except for when i left the 125cc bikes in the dust...) also i was never threatened or felt in any danger at any time. the pakistanis are a welcome relief after india...
if you can handle the BS paperwork in india, once you reach turkey you will feel the time and effort well worth the reward.