Shop that works with modified bikes?

[monkeyfarm]

Seems close but not identical in regards to mounting points.

82 Sabre


82 Magna

 

[TK4]

(Also, not sure @TK4 needs to prove his 'older toys' credentials! Where's that "cry laughing" emoji?)

They had premature cams, rockers, cam chains and tensioners failures. Most were covered under warranty back in the day, but the first thing i would do is pull the cam covers off and take a look.
My rule #1 - if the bike is older than you are it's a long term project and not a daily rider.