Jaguar rear suspension

I have two XJS’s. One is a 1986 and one is a 1982. The 1986 is in great shape. The 1982 was acquired without an engine or transmission. The body is in a great rust-free condition. I have decided to drop a chevy LT1 into the 1982. (I know don’t say it!). The rear ratios are 2.88 on both cars I believe.
My question to everyone is which year IRS is the stronger of the two. And which year IRS is easier to get parts for. I think the 1986 might be the dana.

The two units are basically the same. One difference could be the speedometer pick up. If the differentials have drain plugs, they are Salisbury.