There are plenty of working used engines. A member here is offering rebuilds for $5k but/and has a reputation for good work. The used engine shouldn't be too difficult to get running on a stand before installing.

Dad used to say "you pays your money and takes your chances. A proper diagnosis before doing anything is important.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.